Browse Topic: Octane

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Effects of Gasoline Composition and Operating Parameters on the Response of End-Gas Autoignition to Nitric Oxide in a Lean-Burn DI-SI Engine2026-01-03134/7/2026
Lean operation of spark-ignition engines can lead to engine thermal efficiency gains and lower NOx emissions due to reduced combustion temperatures. Yet, lean operation could still face challenges in end-gas autoignition and knock generation due to higher intake pressures and trapped NO in the residual gas. This study evaluates the impact of NO on end-gas autoignition for two gasoline fuels with similar octane rating but different composition: high cycloalkane fuel (HCA) and high olefin fuel (HO). Experiments were performed at stoichiometric and lean (λ = 2) conditions and at two engine speeds of 1400 rpm and 2000 rpm. Accompanying chemical kinetics simulations in CHEMKIN revealed that the mechanisms controlling the effect of NO on autoignition are similar λ = 2 and λ = 1, with NO + HO2 = NO2 + OH being the main pathway for enhancing reactivity by promoting low-temperature heat release (LTHR). The compositionally different fuels reacted differently to NO seeding and engine speed, and differences were augmented at λ = 2 compared to λ = 1 as the end-gas autoignition shifted to the low temperature regime. HO, which has inherent low temperature chemistry, was strongly impacted by engine speed at low NO seeding levels, with no noticeable peak of LTHR detected at 2000 rpm. On the other hand, LTHR of HCA was marginally affected by shortened residence time at higher engine speed as NO + HO2 reaction was not greatly affected by shorter time scales, since HO2 production was sustained even at 2000 rpm to support OH generation from NO + HO2. Contrary to HO, HCA exhibited greater sensitivity to NO seeding, as the increased OH production at higher NO concentrations offset the OH-quenching effect of cyclopentane, which accounts for 28.6% of HCA’s composition. Consequently, a sensitivity analysis revealed that fuels with weak inherent low-temperature chemistry, like HCA, are likely to be more sensitive to variations in NO concentration and charge temperature, whereas fuels with strong low temperature chemistry are more sensitive to variations in end-gas λ and intake pressure.
Kim, Namho, Abboud, Rami, Sjöberg, Magnus, Lopez Pintor, Dario, Saggese, Chiara, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota, Sugata, Kenji
Effect of Injector Tip Temperature on Methanol Spray Dynamics during Cold-Start Conditions2026-01-03404/7/2026
Methanol is one of the most readily produced e-fuels and remains in liquid form at ambient conditions, making storage and transportation relatively simple. In the marine sector, methanol has already been actively adopted as a pathway toward carbon neutrality. For automotive sectors, methanol offers significant potential for carbon emission reduction owing to its higher octane number and lower carbon content compared with gasoline. However, its high latent heat of vaporization and low vapor pressure suppress evaporation at low ambient temperatures, leading to increased emissions during cold-start operation. To address this issue, previous studies have explored heating the injector tip or fuel rail to enhance evaporation and atomization. The present study focuses on visualizing and quantifying the improvement in methanol evaporation characteristics under cold-start conditions by applying controlled heating to the injector tip. Experiments were conducted in a constant-volume chamber where the ambient temperature was carefully regulated, while a laterally mounted injector tip was subjected to different heating levels. Extinction images were acquired to determine spatial and temporal liquid volume fraction and to visualize spray morphology and penetration behavior for both methanol and gasoline surrogate fuel E00. Moreover, three-dimensional tomography reconstructed from extinction images taken at multiple viewing angles provided an in-depth assessment of methanol spray structure, droplet distribution, and evaporation behavior with varying injector tip temperatures under simulated cold-start conditions. These findings highlight the crucial role of injector thermal management in improving methanol-fueled engine performance during low-temperature operation.
Lee, Seungwon, Kim, Hyunsoo, Bae, Sumin, Hwang, Joonsik, Bae, Choongsik
Study of Combustion Characteristics of a Two-Stroke Opposed Piston Engine using Low-Octane Fuels2025-32-002811/3/2025
Various fuels are being considered as the next generation of carbon neutral fuels, including methanol, ethanol, and SAF. These have widely different ignition properties. Methanol and ethanol are high-octane fuels, so there are no major problems with their use in gasoline engines. However, SAF is a hydrocarbon with a large molecular weight, so it has a fundamentally low octane rating and is not easy to use in SI engines. In order to put carbon-neutral fuels of various properties into practical use, it is effective to develop a technology that allows fuels with low octane to be operated in SI engines. Therefore, in this study, basic research was conducted on the combustion of fuels with low octane using PRF fuel in opposed-piston engines. Opposed piston engines are characterized by their light weight due to the absence of a cylinder head, low S/V ratio due to the ultra-long stroke, reduced cooling loss due to the long stroke, and reduced vibration due to the offsetting of the reciprocating inertial forces of the left and right pistons, resulting in high efficiency and output. In addition, one of the disadvantages of low-octane fuel is that it tends to auto-ignite, but combustion under high residual gas conditions has the effect of suppressing fuel auto-ignition, and by using a 2-stroke engine with a high percentage and high concentration of residual gas and locally high temperatures, auto-ignition is suppressed and low The use of two-stroke engines with high residual gas content and high concentration and high local temperatures can be expected to suppress auto-ignition and allow the use of low-octane fuels.
Yamazaki, Yoshiaki, Okawara, Ikumi, Liu, Jinru, Iijima, Akira
Bridging Fundamental Combustion Analysis and Engine Knock Behavior -1st Report, CFR Engine Test for Various RON Fuels2025-01-039110/7/2025
A collaborative study was conducted to bridge the gap between fundamental combustion research and engine-scale observations of knock in spark-ignition (SI) engines. Using Primary Reference Fuels (PRFs) with Research Octane Numbers (RON) of 80, 90, and 100, experiments were carried out with a Cooperative Fuel Research (CFR) engine at air-fuel ratio, λ = 1.0, focusing on knock onset conditions in terms of unburned gas pressure and temperature. In the engine tests, pressure traces under knocking conditions were analyzed to identify knock onset and to estimate the corresponding unburned gas temperature history. Results showed that the pressure at knock onset varies clearly with PRF value: higher RON fuels exhibited knock onset at higher pressures, likely due to changes in compression ratio applied to match standard RON test procedures. In contrast, the unburned gas temperature conditions showed partial overlap across different PRFs, but with a tendency for higher RON fuels to experience knock onset at slightly higher temperatures. These findings provide a coherent dataset linking engine-based knock behavior with fundamental combustion characteristics, forming the foundation for the reaction-kinetics-based analysis presented in the second report. Additionally, the CFR engine experiments were also conducted at λ = 0.88 to support the comparison with standard RON measurement conditions.
Yasutake, Yuki, Misono, Katsuhiro, Suzuki, Yoshikatu, Naiki, Taketora, Watanabe, Manabu, Moriyama, Hinata, Morii, Youhi, Tsunoda, Akira, Maruta, Kaoru
Influence of Methanol-to-Gasoline Fuel Formulation on Knock Propensity and Flame Speed2025-01-84004/1/2025
Drop-in gasoline fuels that originate from renewable, low-net-carbon sources, such as methanol-to-gasoline (MTG), are an important bridge in the transition between traditional fossil fuels and electrification of the transportation sector. The composition of these fuels can be tuned by adjusting the settings of the chemical processes used to create them, which can be leveraged to formulate optimized fuels for higher knock resistance or higher flame speed. This study investigated how the distribution of hydrocarbon classes and molecular structure of a renewable MTG gasoline surrogate affected knock and flame speed using chemical kinetic modeling. The original MTG surrogate was modified by increasing the relative amount of a certain hydrocarbon class while the concentration of other hydrocarbon classes is reduced equally. Increasing normal- and iso-alkanes increased reactivity and penalized octane sensitivity, olefins increased octane sensitivity while keeping the research octane number constant, and increasing cyclo-alkanes or aromatics decreased reactivity with the fuel being more sensitive to cyclo-alkanes. To optimize octane rating, short normal-alkanes and long, highly-branched iso-alkanes are preferred, with octane rating being very sensitive to the structure of iso-alkanes. Increased branching also improves octane rating for cyclo-alkanes, olefins, and aromatics. Regarding flame speed, normal-alkanes tend to increase flame speed at engine-relevant conditions because they form radicals that accelerate the flame. However, aromatics and cyclo-alkanes, which are promising octane boosters, showed lower flame speeds. Based on this understanding, an optimized MTG was formulated and compared against the effect of ethanol blending on the original MTG, with the optimized fuel showing similar performance as MTG with 52.5%vol ethanol. Chemical kinetic analyses showed that the chemistry that controls octane rating is different from that that controls flame speed, opening the door to fuels that simultaneously improve both knock and deflagration characteristics.
MacDonald, James, Lopez Pintor, Dario, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota
A Study on Cetane on Demand Technology Part 2: Gasoline Reforming and Ignitability Evaluation2025-01-84444/1/2025
The integration of low-octane gasoline with a compression ignition combustion system has been proposed as a strategy to reduce Well-to-Wheel CO2 emissions from automobiles in petroleum-based fuel. However low-octane gasoline is not widely available in the market currently. Onboard reforming of commercial gasoline to increase the cetane number (lower the octane number) allows for compression ignition combustion even with commercial gasoline. To reform commercial gasoline, a reformer with a spiral structure reactor and mechanical stirring air introduction was designed and prototyped based on the results of toluene reforming tests (A Study on Cetane on Demand Technology Part 1: Development of fuel reformer to improve fuel ignitability). Using N-hydroxyphthalimide (NHPI)-supported ZSM-5 as a catalyst, commercial gasoline was reformed. As a result, 25.5 liters of reformed gasoline was obtained. The hydroperoxide concentration in the entirety of our reformulated gasoline was determined to be 1.5 mmol/L, based on the hydroperoxide concentration measured at each sampling site and the corresponding volume collected. The ignitability of the reformed gasoline was evaluated using an internal combustion engine. Under premixed homogeneous conditions, no difference in ignitability was observed between the gasoline before reforming and the reformed gasoline. However, under non-uniform/diffusion combustion conditions, it was confirmed that the ignitability of the reformed gasoline improved compared to the gasoline before reforming. For the factor analysis, a chemical reaction calculation was conducted, and it was found to be due to the concentration of OH derived from the reformed gasoline. Under diffusion combustion (diesel-like) conditions, the evaluation of engine combustion showed that reformed gasoline expands the lean limit and improves combustion stability in the low-load operating range.
Matsuura, Katsuya, Hashimoto, Kohtaro, Yamada, Yoshikazu, Al-Taher, Maryam, Kalamaras, Christos, Voice, Alexander, Bhadra, Kaustav
Impact of Oxygenated Fuel Components on Engine Performance and Particulate Emissions in Gasoline Blends2025-01-84464/1/2025
The challenges with electrification in the automotive industry have led to rethinking the decisions to ban internal combustion engines. Nonetheless, decarbonization of transportation remains a regulatory priority in many countries, irrespective of the energy source for automotive powertrains. Renewable oxygenated fuel components can help with the rapid decarbonization of gasoline fuels in the current fleet. Ethanol is one of the primary renewable components typically used for blending in gasoline primarily at 10% v/v but up to 20% v/v substitution which corresponds to 3.7 to 8.0% oxygen by mass. However, a range of oxygenates could be used instead of ethanol. This study aimed to determine if the engine could discriminate between different oxygenates in gasoline fuels blended at the same octane (RON) and oxygen levels. Oxygenates such as methyl-tert-butyl-ether (MTBE) and ethyl-tert-butyl-ether (ETBE) were considered in this study. Blends were made using a combination of n-heptane, iso-octane, toluene, and oxygenated components. Seven blends with a nominal RON of 98 +/-2 were evaluated in a single-cylinder engine. Four E10 equivalent and three E20 equivalent fuel blends were studied. The engine was operated at a range of test conditions from throttled, low-load points to boosted, high-load points that required knock retard. The results indicated that all blends had minimal differences in engine performance in terms of knocking behavior, spark timing, burn duration, fuel flow, and injection duration which could all be compensated by the engine control unit (ECU). Particulate matter emissions (AVL micro soot sensor, PN10, PN23) were also evaluated at the test conditions. While the fuels had lower PM-generating components compared to commercial fuels, we could demonstrate that the PM emissions largely correlated with the particulate matter index (PMI) (or the toluene content) of the fuels.
Kalaskar, Vickey, Mitchell, Robert, Pourreau, Daniel
Knock Assessment in Wankel Rotary Engine Adopting Low Octane Rating Fuels2025-01-84524/1/2025
Series hybrid vehicles with internal combustion range extenders are a promising solution for sustainable transportation. In this application, net zero carbon emissions can be achieved using renewable fuels. Fischer-Tropsch-derived e-gasolines/naptha allow for high energy density and safe liquid fuels. However, Fischer-Tropsch naptha fuel derivatives must undergo several processing stages to reach current engine-grade octane ratings, negatively affecting the synthesis's profitability and energy efficiency. Gasoline engine technologies capable of operating with low-octane fuels could allow the adoption of unprocessed Fischer-Tropsch gasoline. The rotary Wankel engine design suits range extenders thanks to its high power-to-size ratio. In this study, the knocking tendency of homogenous charge spark-ignition rotary Wankel engines is numerically assessed through Chemkin-Pro spark-ignition engine zonal model for knock assessment. Rotary Wankel engines are modeled by providing the corresponding time-dependent profiles of volume, wall surface area, wall global heat transfer coefficient, and burnt gas fraction retrieved from previous experimental work. Different engine load conditions have been investigated spanning engine shaft rotational speeds from 3000RPM to 6000RPM and brake mean effective pressures from 3 bar to 7 bar. Detailed kinetic modeling of normal-heptane/iso-octane primary reference fuels is adopted to describe the autoignition tendency of different octane-rating blends. Simulations show a low knocking tendency under the investigated conditions, therefore suggesting the suitability of rotary engines for the adoption of unprocessed Fischer-Tropsch fuels.
Brunialti, Sirio, Vorraro, Giovanni, Turner, James, Sarathy, Mani
A Study on Cetane on Demand Technology Part 1 - Development of Fuel Reformer to Improve Fuel Ignitability2025-01-84474/1/2025
The integration of low-octane gasoline with a compression ignition combustion system has been proposed as a strategy to reduce Well-to-Wheel CO2 emissions from automobiles using petroleum-based fuel. In the current situation where low-octane gasoline is not widely available in the market, onboard reforming of commercial gasoline to increase the cetane number (lower the octane number) allows for compression ignition combustion even with commercial gasoline. This requires “Cetane on Demand” technology, which enables compression ignition combustion with both commercial gasoline and low-octane gasoline. It is known that the ignition property of fuel is enhanced when the fuel is oxidized to generate hydroperoxides. Moreover, the use of N-hydroxyphthalimide (NHPI) as a catalyst promotes hydroperoxide generation at low temperatures. The objective of this study is to develop a device that enhances the ignition properties of gasoline through onboard fuel reforming. Initially, from the seven kinds of NHPI-supported solid catalysts, a catalyst appropriate for a flow reactor operating at ambient pressure was selected. The NHPI-supported ZSM-5 catalyst demonstrated the highest performance in hydroperoxide formation under flow reactor conditions. Subsequently, with a focus on onboard reforming, two types of reactors (spiral-type reactor and inner-circulation type reactor) and two methods of air introduction (metal mesh bubbler and mechanical stirring bubbler) to ensure adequate contact between the fuel, air, and solid catalyst were designed and prototyped. The combination of the spiral-type reactor and mechanical stirring air introduction exhibited the best performance in hydroperoxide formation.
Hashimoto, Kohtaro, Yamada, Yoshikazu, Matsuura, Katsuya, Kudo, Tomohide, Chishima, Hiroshi, Al-Taher, Maryam, Kalamaras, Christos, Albashrawi, Reem
Effects of Fuels Properties on Combustion and Emissions Characteristics of Light Duty GCI Engine2024-01-427911/5/2024
Our research group developed Gasoline Compression Ignition (GCI) fuel matrix based on the fuel properties, specifications and fuel sources in an effort to standardize the GCI fuel. This study attempts to experimentally validate the standardized GCI fuels to comply with the operational regimes of GCI engine. Two of the formulated GCI fuels (GCI7 and GCI8) with varying physical and chemical properties, and composition were investigated in a single cylinder compression ignition (CI) engine. In addition to fuel effects, the engine variables were parametrically varied at low (3 bar IMEP) and medium (7 bar IMEP) load conditions. At low loads, the fuel chemical effects played a crucial role in governing the combustion while physical effect had a negligible impact. Due to lower cetane number of GCI8 fuel, combustion is predominantly premixed for GCI8 fuel but GCI7 fuel shows a more pronounced diffusion combustion phase. The low temperature heat release (LTHR) is evident only for GCI8 fuel due to higher octane rating (RON = 60) whereas GCI7 fuel (diesel like) showed negligible LTHR phase. Despite improvements in engine operating parameters, the combustion performance of GCI8 is lower than GCI7 fuel. However, after improving the fuel injection strategies, GCI8 fuel showed improved peak in-cylinder pressure and heat release compared to GCI7 fuel. Double injection advanced the combustion phasing, shortened the ignition delay, and improved the burn rate when compared to single injection. Fuel composition played a crucial role in emission formation in that smoke emission is increased for GCI7 due to higher fraction of aromatics in the fuel compared to GCI8. The increased premixed effect due to lower cetane number of GCI8 decreased the fuel to air equivalence ratio and in-cylinder temperature in that NOX emission is reduced.
Qahtani, Yasser Al, Raman, Vallinayagam, Viollet, Yoann, Alhajhouje, Abdullah, Cenker, Emre, AlRamadan, Abdullah
Performance Evaluation of High Octane Gasoline Fuel(s) on High Compression Ratio (HCR) Motorcycle – Based on Chassis Dynamometer Test2024-01-23754/9/2024
The present study aims to determine the comparative performance evaluation in terms of fuel economy (kmpl) and wide open throttle (WOT) power derived from set of different blends of high octane gasoline fuel(s) i.e., Neat Gasoline (E0), E10 & E20 (With different dosages of additives) in high compression ratio (HCR) motorcycle on chassis dynamometer facility. With the Government of India focus on use of alcohol as co-blend of gasoline with the endeavour to save foreign exchange and also to reduce greenhouse gases (GHG) emissions. The commercially available blended fuels, E10 & E20, have high research octane number (RON, 92-100) and as per the available literature high RON fuel have the better anti-knocking tendencies thereby lead to higher fuel economy. There are various routes to formulate high octane fuel (refining technologies, additive approach & ethanol blending route) in the range of 92-100 octane number which are currently commercialized in Indian market. In the present study, ethanol based high octane fuel blend(s) along with doping of novel indigenous type of additives (multifunctional additive & octane booster) to achieve the utilization benefits in terms of fuel economy (FE) & power improvement. The findings of present study largely suggest that with the high octane fuel blends (only ethanol) the fuel economy and Wide Open Throttle (WOT) power reduces. On the other hand, by adding gasoline multi-functional additive (GMFA) in combination of octane booster in the ethanol blended fuels, fuel economy and WOT power are compensated fairly. Fuel economy and Wide Open Throttle (WOT) power were investigated under operating conditions (Indian driving cycle - IDC). On adding ethanol only by 10% and 20% in gasoline the fuel economy is lowered by 1.9% and 4.94% respectively. The loss in fuel economy is reduced by 0.74% and 3.36% through addition of indigenously developed GMFA with Octane Booster in E10 & E20 gasoline blends.
Saroj, Shyamsher, Kalita, Mrinmoy, Kumar, Prashant, Kant, Chander, Patanwal, Pradeep, Chakradhar, Maya, Sithananthan, M, Arora, Ajay Kumar, Harinarain, Ajay Kumar, Maheshwari, Mukul
Effect of Cyclo-Pentane Impurities on the Autoignition Reactivity and Properties of a Gasoline Surrogate Fuel2024-01-50212/16/2024
Surrogate fuels that reproduce the characteristics of full-boiling range fuels are key tools to enable numerical simulations of fuel-related processes and ensure reproducibility of experiments by eliminating batch-to-batch variability. Within the PACE initiative, a surrogate fuel for regular-grade E10 (10%vol ethanol) gasoline representative of a U.S. market gasoline, termed PACE-20, was developed and adopted as baseline fuel for the consortium. Although extensive testing demonstrated that PACE-20 replicates the properties and combustion behavior of the full-boiling range gasoline, several concerns arose regarding the purity level required for the species that compose PACE-20. This is particularly important for cyclo-pentane, since commercial-grade cyclo-pentane typically shows 60%–85% purity. In the present work, the effects of the purity level of cyclo-pentane on the properties and combustion characteristics of PACE-20 were studied. Chemical kinetic simulations were performed to predict the effects of cyclo-pentane impurities on the properties, octane rating, and autoignition reactivity under homogeneous charge compression-ignition conditions of PACE-20. From the numerical results, cyclo-pentane with 85% purity or higher is required to reasonably match both the research octane number and motor octane number of the target gasoline. Finally, homogeneous charge compression-ignition engine simulations show that impurities have only a modest effect on reactivity at naturally aspirated conditions, but cyclo-pentane purity is critical to properly replicate the pressure dependency of the reactivity.
Lopez-Pintor, Dario, Abboud, Rami, MacDonald, James, Lee, Sanguk
Dynamic Spark Advance Technology for Gasoline Fuel Blends2024-26-00741/16/2024
Fuel efficiency is one of the most important customer requirement in Indian market as well as very crucial to meet the upcoming regulation like CAFÉ for Indian Automotive manufacturers. Most of the technology changes to meet this challenge, always come with a cost penalty with hardware addition. To counter the above challenge, a strategy has been identified in the EMS software that will dynamically adapt the spark timing based on fuel octane rating. This strategy has resulted in fuel efficiency improvement on Modified Indian Drive Cycle on chassis dynamometer test and as well as on real life road tests using fuels with various octane number.
Tyagarajan, Sethuramalingam, Kavekar, Pratap, Suna, Bhagyashree, Agarwal, Nishant, Shaikh, Wasim
Reduced Carbon Intensity of Ethanol Blend Gasoline13-05-02-001010/26/2023
Tank-to-wheels (TTW) CO2 reduction for ethanol blends is determined from either gasoline composition or vehicle exhaust measurements. Fuels are characterized using a carbon intensity (CI), which is the ratio of carbon (as CO2 mass) in the fuel to the net heating value. Our objective is to assess changes in CI of market gasoline with varying ethanol content that can be used to appreciate change in vehicle tailpipe greenhouse gases (GHG) in response to policy controlling the ethanol level in market fuels. Ethanol has both a reduced carbon content and a reduced net (lower) heating value relative to petroleum species, with a CI slightly lower than that of typical petroleum gasoline. However, ethanol blending offers additional CI reduction because it enables a reduction of aromatics in the petroleum blendstock for oxygenate blending (BOB) while maintaining octane rating of the blend. Aromatics have a CI about 20% higher than paraffins. The primary refinery option for aromatic reduction is through lower severity or throughput for the gasoline reformer, which ultimately reduces CI in the BOB and the finished blend. Expected gasoline market blends were projected by developing a model that addressed US refining and blending in response to octane requirements. A TTW blending CI, or BCI, for ethanol is proposed to describe the total CI reduction in the finished blend enabled by the ethanol. The ethanol BCI was found to average at 59 gCO2/MJ for E10, E15, and E20 (10%, 15%, and 20% ethanol by volume) market fuels in this study. This is substantially below the ethanol chemical CI of 71.0 gCO2/MJ and petroleum CI of 73.5 g CO2/MJ due to the enabling of aromatic reduction. E10 in comparison to E0 (purely petroleum) is estimated to offer a national US tailpipe CO2 reduction of 16.6 billion kg annually.
Clark, Nigel N., Klein, Tammy, Higgins, Terrence, McKain, David
Evaluation of Fully Sustainable Low Carbon Gasoline Fuels Meeting Japanese E10 Regular and Premium Octane Specifications2023-32-01659/29/2023
Reducing the carbon emissions associated with ICE- containing vehicles is a complimentary step towards carbon neutrality alongside the introduction of vehicles using newer energy vectors. In this study, the authors investigated emissions and efficiency impact of fully renewable E10-grade gasoline fuels blended with sustainable components at both 90 RON and 96 RON in comparison with reference regular E0 and premium certification gasolines across a range of ICE vehicle applications. Both renewable fuels were blended to the Japan JIS K2022 2012 E10 specification. The study shows very low carbon gasolines are technically feasible and potentially have an important role to play in decarbonizing both new advanced technology ICE vehicles and, critically, the existing ICE vehicle parc in the transition towards a zero emissions future.
Yates, Timothy, Ali, Rana, Suzuki, Mayu, Matsubara, Naoyoshi, Yokoo, Nozomi, Morii, Takuya, Akiyama, Shota, Ishizaki, Keita
Explicit equations for designing surrogate gasoline formulations containing ethanol, isopentane, n-heptane, isooctane and toluene2023-32-01649/29/2023
It is useful for research purposes to define simple surrogate gasoline compositions that can replicate the chemical and physical properties of more complex mixtures. Ethanol is used in commercially available gasolines around the world as part of the pathway to the decarbonization of the transportation sector. In this study equations were developed to predict the Research Octane Number (RON), Motor Octane Number (MON) and Dry Vapour Pressure Equivalent (DVPE) of gasoline surrogates containing ethanol (10-25 vol%), isopentane, n-heptane, isooctane and toluene. The non-linear blending behaviour associated with ethanol is found to necessitate coefficients in the equations developed for MON that are a function of ethanol content, whereas surprisingly the equations for RON and DVPE do not need this added level of complexity. Using the equations developed the RON and DVPE of the ethanol-containing surrogates can be calculated using one set of coefficients for any ethanol concentration between 10 and 25 vol%. Calculating the MON of such surrogates requires different sets of coefficients for different ethanol concentrations.
Kaliafetis, Filimonas, Cracknell, Dr. Roger F.
Fuel Effects on the Onset of Knock and the Intensity of Superknock at Stochastic Preignition-Relevant Engine Conditions03-17-02-00109/5/2023
To have a more complete understanding of the fuel effects on each subsequent stage of a stochastic preignition event in a spark-ignition engine and to build on the previous work of understanding the propensity of fuel to initiate and sustain a preignition flame, this work is focused on examining the role of fuel on the onset of knock and the intensity of superknock once the unburned mixture reaches certain conditions ahead of the preignition flame. Using a “skip advance” spark test method to simulate preignition flames initiated at different cylinder conditions, more than 20 single- and multicomponent fuels were ranked based on the condition required to reach the onset of knock (the start of end-gas autoignition) and the condition that leads to severe superknock intensities. It was found that average knock intensity can be mainly explained by the unburn mixture fraction and the thermodynamic condition of the unburned mixture and, not surprisingly, that the fuel ranking for the onset of knock and superknock based on average knock intensity is correlated to octane index. However, outlier cycles with extremely high knock intensities cannot be fully explained by the average cycle behavior. More interestingly, different fuels exhibit different superknock characteristics. Some fuels, such as toluene, have fewer extreme cycles once the same average knock intensity condition is reached, whereas other fuels, such as ethanol, have more extreme cycles that tend to break engine hardware in a single cycle event. A preliminary study based on the modes of reaction front propagation show that fuels with low-temperature heat release and negative temperature coefficient (NTC) behavior can lead to a higher propensity to produce extreme knock intensities when coupled with the right in-cylinder pressure wave.
Yu, Xin, Costanzo, Vincent, Chapman, Elana, Davis, Richard
Correlation of Oil Originating Particle Emissions and Knock in a PFI HD SI Engine Fueled with Methanol2023-24-00368/28/2023
A viable option to reduce global warming related to internal combustion engines is to use renewable fuels, for example methanol. However, the risk of knocking combustion limits the achievable efficiency of SI engines. Hence, most high load operation is run at sub-optimal conditions to suppress knock. Normally the fuel is a limiting factor, however when running on high octane fuels such as methanol, other factors also become important. For example, oil droplets entering the combustion chamber have the possibility to locally impact both temperature and chemical composition. This may create spots with reduced octane number, hence making the engine more prone to knock. Previous research has confirmed a connection between oil droplets in the combustion chamber and knock. Furthermore, previous research has confirmed a connection between oil droplets in the combustion chamber and exhaust particle emissions. However, the co-variation between oil originating particle emissions and knock has not been investigated. The current study examines the connection between knock and particle number in the exhaust, when running on fuel with low soot production. A single cylinder spark ignited heavy-duty engine was used. It was equipped with port fuel injection and fueled with methanol, which produces very little soot at lambda 1. Consequently, the measured exhaust particle numbers were assumed to origin essentially from engine oil. Three grades of oil, in combination with three piston ring configurations, were used to vary the amount of oil entering the combustion chamber. Results from knock limited operation at both medium and high engine load showed that an increased number of particles in the exhaust was associated with an increased likelihood of knock. The authors find the hypothesis that an increase in particle number correlates with an increase in auto-ignition tendency to be confirmed.
Ainouz, Filip, Adlercreutz, Ludvig, Cronhjort, Andreas, Stenlaas, Ola
Methanol Evaporation in an Engine Intake Runner under Various Conditions2023-24-00188/28/2023
Methanol has recently emerged as a promising fuel for internal combustion engines due to its multiple carbon-neutral production routes and advantageous properties when combusting. Methanol is intrinsically more suitable for spark-ignition (SI) operation thanks to its high octane number, but its potential in heavy-duty applications also encourages engine manufacturers in this field to retrofit their existing compression-ignition products into methanol/diesel dual-fuel (DF) operation. For both SI operation and DF operation, injecting methanol into the engine’s intake path at low pressure is a relatively simple and robust method to introduce methanol into the cylinders. However, the much higher heat of vaporization (HoV) of methanol compared to conventional SI fuels like gasoline can be a double-edged sword. On the one hand, its enhanced cooling effect may increase volumetric efficiency and lower knock tendency, on the other hand, the extra heat it absorbs when evaporating may pose cold-start issues and lead to unstable combustion. To further investigate, a special experimental setup was built. Multiple thermocouples were mounted on an intake runner where the fuel is injected to monitor the temperature changes of the flow before and after injection. The temperature of the runner itself was also monitored to assess the heat taken from the metal wall of the runner pipe. Different air-fuel ratios, air temperatures, air pressures, and air mass flow rates were tested to evaluate their influences on methanol evaporation. The test results were then compared with conventional gasoline operation. It was found that the temperature drop after fuel injection is strongly dependent on the flow temperature, and that the evaporated fraction of methanol was far lower than that of gasoline even with higher flow temperature. Their very different evaporation behaviors are thoroughly discussed.
Pu, Yi-Hao, Larsson, Tara, Robeyn, Tom, De Paepe, Michel, Verhelst, Sebastian
Effects of Pre-spark Heat Release of Ethanol-Blended Gasoline Surrogate Fuels on Engine Combustion Behavior04-17-01-00035/2/2023
Regulations limiting greenhouse gas (GHG) emissions in the transport sector have become more restrictive in recent years, drawing interest to synthetic fuels such as e-fuels and biofuels that could “decarbonize” existing vehicles. This study focuses on the potential to increase the thermal efficiency of spark-ignition (SI) engines using ethanol as a renewable fuel, which requires a deep understanding of the effects of ethanol on combustion behavior with high compression ratios (CRs). An important phenomenon in this condition is pre-spark heat release (PSHR), which occurs in engines with high CRs in boosted conditions and changes the fuel reactivity, leading to changes in the burning velocity. Fuel blends containing ethanol display high octane sensitivity (OS) and limited low-temperature heat release (LTHR). Consequently, their burning velocities with PSHR may differ from that of gasoline. This study therefore aimed to clarify the effects of ethanol on SI combustion behavior under PSHR conditions. Combustion behavior was studied by performing single-cylinder engine experiments and chemical kinetics simulations. The experimental measurements were performed to characterize the relationship between the occurrence of PSHR and the main combustion duration. Analysis of this relationship showed that the ethanol-blended fuel has a lesser PSHR and a longer combustion duration than the non-ethanol fuel by approximately 5% in high engine load conditions. Simulations using input data from the experiments revealed that the ethanol-blended fuel has a lower laminar burning velocity due to the lower temperature in the unburned mixture caused by its PSHR. Additional simulations examining the chemical effect of partially oxidized reactants caused by PSHR on the laminar burning velocity showed that partially oxidized reactants increase the laminar burning velocity of the ethanol-blended fuel but decrease that of a reference fuel without ethanol. A large number of fuel radicals and oxides of the ethanol-blended fuel enhances chain-branching reactions in the pre-flame zone and possibly increases its laminar burning velocity. However, the thermodynamic effect of PSHR on laminar burning velocity exceeds the chemical effect, and thus the ethanol-blended fuel has a lower turbulent burning velocity in the PSHR conditions.
Yoshimura, Kei, Isobe, Kohei, Kawashima, Mitsutaka, Yamaguchi, Kyohei, Sok, Ratnak, Tokuhara, Satoshi, Kusaka, Jin
Gasoline, Alcohol, and Diesel Fuel Surrogates for Materials TestingJ1681_202305 (Current)5/1/2023
This SAE Recommended Practice presents recommendations for test fuels and fluids that can be used to simulate real world fuels. The use of standardized test fluids is required in order to limit the variability found in commercial fuels and fluids. Commercial fuels can vary substantially between manufacturers, batches, seasons, and geographic location. Further, standardized test fluids are universally available and will promote consistent test results for materials testing. Therefore, this document: a Explains commercial automotive fuel components b Defines standardized components of materials test fluids c Defines a nomenclature for test fluids d Describes handling and usage of test fuels e Recommends fluids for testing fuel system materials The test fluid compositions specified in Section 7 of this document are recommended solely for evaluating materials. They are not intended for other activities, such as engine development, design verification, or process validation unless agreed upon by the contracting parties. Most marketplace fuels contain additives for such purposes as oxidation stability, intake and combustion chamber deposit control, anti-foaming, electrostatics, octane, corrosion mitigation, etc., applied at a parts per million basis. It is not the intention of this document to include a surrogate for the potential effects of these additives. As far as this committee is aware, current additives do not adversely affect fuel system materials. Those contemplating new or improved additives for future applications could use the basic test fluids or fuels from this document, and specify the fuel is to be unadditized in order to inject such additives and use the resulting mixtures to assess whether these new additives might affect fuel system materials. For the purposes of this document, the term FUEL is used in conjunction with fully blended hydrocarbon or hydrocarbon oxygenate mixtures for use in commercial automotive engines. The term FLUID is applied to mixtures of specific controlled components used to simulate the effects of fuels.
Fuel Systems Standards Committee
Material Compatibility of Elastomers and Plastics in Gasoline- Ethanol-Methanol Blends2023-01-03364/11/2023
The current Indian biofuel policy focuses on the use of alcohol as a potential gasoline blending component to achieve a target of 20% alcohol in gasoline by 2025. The automotive vehicle fuel system uses a variety of metals and non-metals (elastomers and plastics). The fuel system is designed to run with a dedicated fuel, say gasoline or diesel. The use of alternative fuels, i.e., fuels that blend with straight gasoline or diesel, is increasing, and it is critical to understand the impact of these fuels on engine fuel system components. High octane fuels like ethanol and methanol are blended with gasoline to increase engine performance and reduce exhaust emissions, but the alcohols are hygroscopic and corrosive in nature. These fuels' permeation, swelling, and other effects cause changes in material properties. The test fuel is a gasoline-ethanol-methanol (GEM blend of A20 blend), which contains 5% ethanol, 15% methanol, and 80% gasoline. There is no data available on the use of A20 in the Indian context. Hence, there is a need to assess these materials for compatibility issues with the A20 fuel for the intended design life or if there is a modification in the fuel system components. Material compatibility studies were carried out on materials used in components as per the guidelines given in SAE J 1748 for non-metal (elastomers and plastics) compatibility studies, which are specific for hydrocarbon fuels and their mixtures with oxygenated additives. The sample coupons are immersed in the test fuel at 55 °C in the oven for a period of 1008 hours for elastomers and 3024 hours for plastics. The material properties of elastomers (FKM, NBR, NBR-PVC, and ECO) and plastic material PA66 are evaluated before and after immersion to assess the impact of ageing on materials. The change in behaviour of materials—weight, volume, tensile strength, elongation, and hardness—is elaborately discussed. ECO (wet) and NBR (wet) show better performance in gasoline, and the rest of the elastomers show better or similar performance in all the properties with A20 and E10 fuels. ECO (wet) and NBR (wet) have shown better performance in gasoline, and the rest of the elastomers (FKM and NBR-PVC) show better or similar performance with E10 compared to A20. This study has revealed the material compatibility with the A20 fuel vis-a-vis gasoline/E10 fuels.
Chakradhar, Dr. Maya, Ramadhas, A S, Shanti, Prakash, Justin, P Raj, Arora, Ajay, Maheshwari, M
Combustion Regimes in the Chrysler Multi-Air Multi-Fuel Engine, Part 1 - Diesel Assisted Spark Ignited2023-01-02314/11/2023
This paper is the first of three papers stemming from a dual fuel Chrysler prototype engine which uses both diesel and gasoline direct injection running at stoichiometric conditions, as part of a project to explore the viability of incorporating an engine platform which utilizes low temperature combustion regimes into a modern automotive application. The combustion system used high rates of EGR while maintaining combustion stability by using high charge motion intake port and a high energy ignition system. The engine ran highly dilute SI combustion at low loads, Diesel Assisted Spark Ignition at medium loads and a transition to Diesel Micro Pilot ignition at medium to high load. This paper explores diesel assisted spark ignited combustion at medium loads 6.5 bar to 12.7 bar BMEP. The second paper will explore the use of diesel micro-pilot ignition at high loads 10.6 bar to 14.5 bar BMEP and the third paper to be published in 2024 will explore fuel property effects (mainly Cetane and Octane) through the use of alternative fuels. In the diesel assisted spark ignited combustion regime combustion is initiated via a spark while using a diesel injection to provide a low octane fuel source early in combustion. Results were obtained at speed/load points ranging from 1500 to 3200 RPM and boost levels ranging from 95 to 200 kPa. Spark timing, diesel injection timing, and exhaust gas recirculation percentage were crucial variables affecting the performance of the engine. Brake thermal efficiency levels above 39% were possible at numerous operating conditions.
Church, William, McConnell, Steven
Ignition Delay Time of a Toluene Reference Fuel with Substituted Phenol Additives2023-01-03214/11/2023
Rapid compression machines can be used to measure a fuel’s ignition delay time and develop an understanding of its resistance to autoignition. Continuing developments in engine design demand higher octane fuels that are resistant to autoignition. Substituted phenols are members of the aromatic hydrocarbon family, and aromatics like toluene are often added to pump-grade gasoline to increase the fuel octane number. Previous numerical and experimental studies have found that substituted phenols included at additive levels in gasoline surrogates, such as the toluene reference fuel in this study, may have a lengthening effect on the ignition delay time of the base fuel they are added to. In this study, the substituted phenols 2,4-xylenol and 3,5-xylenol were added to their own respective toluene reference fuel at 2% by mole, and the ignition delay times of the base fuel mixtures including substituted phenols were compared to the base fuel without additives at engine-relevant conditions for equivalence ratios of φ = 0.6, 0.8, and 1.0. In combination with fuel composition, exhaust gas recirculation has been used to lengthen the ignition delay time of fuel-air mixtures, where exhaust gas recirculation helps to inhibit autoignition of fuel-air mixtures by lowering the combustion temperature of the mixture. The effect of exhaust gas recirculation on the ignition delay time of different fuel compositions was studied by using nitrogen as a diluent. Exhaust gas recirculation was carried out by adding N2 at rates of 15% and 30% for the stoichiometric fuel-air mixtures. Both additives were found to lengthen the ignition delay of the toluene reference fuel at high and low temperatures, but not at mid-range temperatures. 2,4-xylenol had a lengthening effect on the toluene reference fuel at more conditions than 3,5-xylenol did.
Trombley, Grace, Toulson, Elisa
Split Injection of High-Ethanol Content Fuels to Reduce Knock in Spark Ignition2023-01-03264/11/2023
Spark ignition engines have low tailpipe criteria pollutants due to their stoichiometric operation and three-way catalysis and are highly controllable. However, one of their main drawbacks is that the compression ratio is low due to knock, which incurs an efficiency penalty. With a global push towards low-lifecycle-carbon renewable fuels, high-octane alternatives to gasoline such as ethanol are attractive options as fuels for spark ignition engines. Under premixed spark ignition operating conditions, ethanol can enable higher compression ratios than regular-grade gasoline due to its high octane number. The high cooling potential of high-ethanol content gasolines, like E85, or of ethanol-water blends, like hydrous ethanol, can be leveraged to further reduce knock and enable higher compression ratios as well as further downsizing and boosting to reduce frictional and throttling losses. In this work, a split injection strategy is used, where 5-15% of the total injected fuel is injected during the compression stroke with E75 gasoline (75% ethanol, by volume) and hydrous ethanol (190 proof ethanol, 92% ethanol, 8% water, by mass). These experimental results indicate that injecting a small amount of E75 or WE92 during the middle of the compression stroke such that the fuel cannot completely homogenize with the air before the spark fires results in knock mitigation that exceeds the amount of knock mitigation expected by evaporating that amount of fuel in air in a premixed setting. This split injection strategy achieved a 1.3% relative fuel conversion efficiency benefit with E75 at 19 bar IMEPn and a 1.4% relative fuel conversion efficiency benefit at 15 bar IMEPn with WE92. Overall, these results indicate that a split injection strategy with a high cooling potential alcohol fuel can further increase a fuel’s effective octane number, enabling highly boosted, high compression ratio stoichiometric spark ignition operation.
Gainey, Brian, Gandolfo, John, Gao, Mingyang, Lawler, Benjamin
Optimizing Spark Assisted GCI Combustion with the Compression Ratio and Internal Exhaust Gas Recirculation (I-EGR) Strategies2023-01-02264/11/2023
The combustion instability at low loads is one of the key technology risks that needs to be addressed with the development of gasoline compression ignition (GCI) engine. The misfires and partial burns due to combustion instability leads to excessive hydrocarbon (HC) and carbon monoxide (CO) emissions. This study aims to improve the combustion robustness and reduce the emissions at low loads. The GCI engine used in this study has unique hardware features of a spark plug placed adjacent to the centrally mounted gasoline direct injector and a shallow pent roof combustion chamber coupled with a bowl in piston geometry. The engine experiments were performed in a single cylinder GCI engine at 3 bar indicated mean effective pressure (IMEP) and 1500 rpm for certified gasoline with research octane number (RON) = 91. Enabling strategies such as internal exhaust gas recirculation (i-EGR), compression ratio (CR = 16 & 18) and spark assisted ignition were investigated to improve the combustion robustness. Several other control variables such as intake temperature, intake pressure, fuel injection pressure, fuel injection timing, and exhaust back pressure were used to optimize the operation under low load conditions. The experimental study revealed that exhaust rebreathing supports the combustion stability but with the difficulty of precise back pressure control. For CR = 16 piston, exhaust re-breathing (i-EGR) combined with spark assistance enables to achieve a coefficient of variation (COV) below 2% with NOX emission of around 0.1 g/kWh. At higher CR = 18, pressure and temperature conditions are favorable to support the auto-ignition driven combustion without exhaust rebreathing. For improved combustion stability, spark assistance is needed with CR = 18 piston. Optimum spark shortened the burn rate, improved the combustion stability, and reduced the HC emissions. The effects of the flame initiated by the spark plug on the overall combustion is limited to the vicinity of spark arc. Overall, when fuel mixture is stratified under partially premixed compression ignition (PPCI) conditions, spark is needed to strengthen the ignition behavior without disturbing the major auto-ignition combustion behavior.
Raman, Vallinayagam, Viollet, Yoann, Chang, Junseok
Development of a Novel Drop-in Naphthenic Spark Ignition Biofuel by Means of a Fuel Blend Calculator and a Simplified Octane Number Verification Method2023-01-03174/11/2023
In the search for sustainable transportation fuels that are not in competition with food production, considerable efforts are made in the development of so-called second-generation (2G) biofuels. This paper looks into the results of a novel 2G biofuel production technique that is based on a catalytic process that operates at low temperature and that converts woody biomass feedstock into a stable light naphtha. The process development is integrated in the Belgian federal government funded Ad-Libio project and the process outcome is mainly consisting of hydrocarbons containing five to six carbon atoms. Their composition can be altered, resulting in a large amount of different possible fuel blends. The ultimate goal is to produce a drop-in fuel that can be fully interchanged with the gasoline fuels in use today. This is a challenge, since the Ad-Libio fuel components differ significantly from gasoline fuel components. For an initial assessment of the suitability of a novel blend, a fuel blend calculator with integrated fuel database has been developed. This tool enables fast SI fuel property calculations, so quick decisions can be made on the fuel production process outcome. The blend’s research octane number (RON) is one of the important properties to be checked for a blend’s suitability as a spark ignition engine fuel. After a first screening with the calculator, the average peak pressure pulsation (APPP) method was used on a CFR engine to evaluate the octane number of the blends, enabling quick in-house experimental octane number verification of the calculations before the blends can ultimately be sent to an ASTM-compliant testing laboratory. This article describes the calculation and verification methodology of the first blends that have been used to design a new and fully sustainable SI engine fuel blend, ultimately aiming for a sustainable second-generation drop-in gasoline fuel replacement.
Robeyn, Tom, Larsson, Tara, Demeersseman, Jonathan, Van Biesen, Jonas, Verhelst, Sebastian
Experimental Study on Flash Boiling of Ammonia Fuel Sprays – A Potential Alternative Fuel2023-01-03044/11/2023
The current transportation fuels have been one of the biggest contributors towards climate change and greenhouse gas emissions. The use of carbon-free fuels has constantly been endorsed through legislations in order to limit the global greenhouse gas emissions. In this regard, ammonia is seen as a potential alternative fuel, because of its carbon-free nature, higher octane number and as hydrogen carrier. Furthermore, many leading maritime companies are doing enormous research and planning projects to utilize ammonia as their future carbon-free fuel by 2050. Flash boiling phenomenon can significantly improve combustion by enhancing the spray breakup process and ammonia possessing low boiling point, has a considerable potential for flash boiling. However, present literature is missing abundant research data on superheated ammonia sprays. Therefore, this research work aims to optically investigate the behavior of ammonia sprays under different conditions of fuel temperatures for varying chamber pressures. This work probes overall ammonia spray geometry at engine relevant conditions and compare the results with gasoline sprays. A multi-hole solenoid gasoline injector is used to inject fuels into a constant volume spray chamber and fuel sprays are investigated using optical z-type schlieren imaging technique. Higher fuel temperatures are achieved by installing a heater coil on the injector tip with a sleeve in between to avoid possible heat transfer losses. The experimental results show significant effect of superheating on ammonia and gasoline sprays. The liquid and vapor phase are clearly characterized upon flash boiling, resulting in decreased spray tip penetration and areas compared to ambient fuel temperature conditions. The results also show differences between the overall spray geometries of both fuels, and that ammonia sprays are more sensitive to chamber pressure as compared to gasoline.
Akram, Muhammad Saad, Yeganeh, Maryam, Cheng, Qiang, Kaario, Ossi, Larmi, Martti
Combustion Regimes in the Chrysler Multi-Air Multi-Fuel Engine, Part 2 - Diesel Micro-Pilot Combustion2023-01-02224/11/2023
This paper is the second of three papers stemming from a dual fuel Chrysler prototype engine which uses both diesel and gasoline direct injection running at near-stoichiometric conditions, as part of a project to explore the viability of incorporating an engine platform which utilizes low temperature combustion regimes into a modern automotive application. The combustion system was designed to tolerate high rates of EGR while maintaining combustion stability by using high charge motion intake port and a high energy ignition system. The engine ran on highly dilute SI combustion at low loads, Diesel Assisted Spark Ignition at medium loads and a transition to Diesel Micro Pilot ignition at medium to high load. The first paper explored the use of Diesel Assisted Spark Ignited at moderate loads 6.5 bar to 12.7 bar BMEP and the third paper to be published in 2024 will explore fuel property effects (mainly Cetane and Octane) through the use of alternative fuels. This paper explores the use of DMP at high loads 10.6 to 14.5 bar BMEP. In the Diesel Micro-Pilot mode, a small quantity diesel injection is used to initiate the combustion of a gasoline-air mixture. Testing was accomplished for engine speeds of 2000 RPM and 2400 RPM with boost levels of 180 kPa to 220 kPa. The engine was optimized to operating points using diesel injection timing and diesel percentage of total fuel mass. Results are presented for both brake thermal efficiency and emissions data. The engine produced brake thermal efficiency levels of 40%.
Church, William, McConnell, Steven
An Experimental Investigation of Directly Injected E85 Fuel in a Heavy-Duty Compression Ignition Engine2022-01-10508/30/2022
A commercially available fuel, E85, a blend of ~85% ethanol and ~15% gasoline, can be a viable substitute for fossil fuels in internal combustion engines in order to achieve a reduction of the greenhouse gas (GHG) emissions. Ethanol is traditionally made of biomass, which makes it a part of the food-feed-fuel competition. New processes that reuse waste products from other industries have recently been developed, making ethanol a renewable and sustainable second-generation fuel. So far, work on E85 has focused on spark ignition (SI) concepts due to high octane rating of this fuel. There is very little research on its application in CI engines. Alcohols are known for low soot particle emissions, which gives them an advantage in the NOx-soot trade-off of the compression ignition (CI) concept. Therefore, the main objective of this research is to experimentally characterise the impact of E85 on performance and emissions of a heavy-duty (HD) direct ignition compression ignition (DICI) engine at mid-to-low load, and to identify possible challenges. To do so, a surface response method of the Box-Behnken type is implemented on a measurement campaign on a HD single cylinder CI engine. The effects of common rail pressure (Prail), λ and combustion timing (CA50) as control parameters on experimentally measured values of soot, regulated gaseous emissions (NOx, CO and THC) and gross indicated efficiency (GIE) of the engine are studied. Linear regression (LR) analysis indicates that the outputs of the NOx and soot models are affected by all three control parameters, whereas GIE, THC and CO models in this case exclude λ effects. E85 fuel shows potential to be a good candidate for highly efficient low temperature combustion (LTC) in DICI engines, with reduced NOx and soot levels compared to fossil diesel combustion.
Novakovic, Maja, Tuner, Martin, Garcia, Antonio, Verhelst, Sebastian
The Impact of Octane Number Boosters on Knock Characteristics in a Cooperative Fuel Research (CFR) Engine2022-01-10828/30/2022
In this study, fuel octane number boosters such as toluene, ethanol, methanol, 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) are blended with primary reference fuels (PRFs) in a cooperative fuel research (CFR) engine at research octane number (RON) relevant conditions. In addition to RON determination, engine operation is characterized by measuring (i) cylinder, intake and exhaust pressure, (ii) averaged intake and exhaust temperature, and (iii) air-fuel-ratio. For known fuel blends, the measured RON corresponds well with existing literature. The addition of MF in PRF yields a significant increase in RON and blending octane numbers (indicating booster impact) up to 216. Cylinder pressure fluctuations, the classical definition of knock intensity, are however not consistent, deviating between PRFs and all boosted blends at higher RON values. Moreover, some fuel blends exhibit scarcely any knocking behavior in the test conditions. The differences cannot be explained purely by ignition delay time, whereas blend-specific flame propagation rate may have an impact. Measurements with two opposing pressure sensors indicate that pressure fluctuations are generally stronger at the spark plug vicinity. With the exception of magnitude, knock amplitude spectra are highly similar with different fuels and the two sensors. The results provide insights into the characteristics and limitations of the CFR engine in the context of such modern octane number boosters, while the detailed measurement data provide a valuable reference for simulations.
Keskinen, Karri, Bhattacharya, Atmadeep, Kaario, Ossi, Blomstedt, Otto, Ranta, Olli, Tripathi, Rupali, Sarjovaara, Teemu
Low Load Ignitability of Methanol in a Heavy-Duty Compression Ignition Engine2022-01-10938/30/2022
An increasing need to lower greenhouse gas emissions, and so move away from fossil fuels like diesel and gasoline, has greatly increased the interest for methanol. Methanol can be produced from renewable sources and eliminate soot emissions from combustion engines [1]. Since compression ignition (CI) engines are used for the majority of commercial applications, research is intensifying into the use of methanol, as a replacement for diesel fuel, in CI engines. This includes work on dual-fuel set-ups, different fuel blends with methanol, ignition enhancers mixed with methanol, and partially premixed combustion (PPC) strategies with methanol. However, methanol is difficult to ignite, using compression alone, at low load conditions. The problem comes from methanol’s high octane number, low lower heating value and high heat of vaporization, which add up to a lot of heat being needed from the start to combust methanol [2]. This paper investigates methanol combustion at low load and compares it to diesel fuel, using a more classical diesel combustion strategy of diffusion combustion. This paper also investigates how a high compression ratio could aid the low load combustion of methanol. To get the methanol burning, with similar stability as diesel fuel, intake heating was used together with a pilot injection, of about a third of the main injection quantity. The resulting efficiencies were similar between diesel fuel and methanol, and for the emission measurements NOx was much lower for methanol than for diesel fuel. Increasing the compression ratio resulted in stable combustion without the need for intake heating and a pilot injection, at even lower loads. It also yielded higher efficiency without having a major effect on the emissions.
Svensson, Magnus, Tuner, Martin, Verhelst, Sebastian
Evaluation of Synthetic Gasoline Fuels and Alcohol Blends in a Spark-Ignition Engine04-15-03-00175/24/2022
Renewable synthetic fuels offer the opportunity to significantly reduce carbon dioxide (CO2) emissions worldwide if burned in the internal combustion engines of existing and future passenger car fleets. To evaluate this potential, two renewable synthetic gasoline fuels and alcohol blends that can be produced via the methanol-to-gasoline (MtG) synthesis process are evaluated in this study. The first synthetic gasoline, hereafter referred to as MtG, was developed by Chemieanlagenbau Chemnitz GmbH and Technische Universität Bergakademie Freiberg, produced within the closed carbon cycle mobility (C3-Mobility) project, and was blended with 10%(V/V) ethanol (MtG-E10), 20%(V/V) ethanol (MtG-E20), 15%(V/V) methanol (MtG-M15), and 15%(V/V) 2-butanol (MtG-2Bu15). The second synthetic fuel, named POSYN (POrsche SYNthetic fuel), was developed by Porsche. The suitability of the synthetic fuels was experimentally investigated in a spark-ignition (SI) single-cylinder research engine with a compression ratio (CR) of 10.8 and compared with conventional gasoline fuel with Research Octane Number 95 and 10%(V/V) ethanol (RON95 E10) gasoline fuel. Load variations at a constant engine speed of 2500 rpm showed no significant differences between Methanol-to-Gasoline with 10%(V/V) ethanol (MtG-E10) and RON95 E10 in terms of both combustion performance and emissions. Additionally, a load variation with MtG-E10 and RON95 E10 at an engine speed of 3000 rpm was performed on a commercially available BMW multi-cylinder engine (MCE), which confirmed that both these fuels show an almost identical combustion and emission behavior. However, the knock resistance improved with higher alcohol fractions. Because of the favorable anti-knock properties of methanol, Methanol-to-Gasoline with 15%(V/V) methanol (MtG-M15) showed the highest maximum net indicated efficiency of 39.33%. This is 2% more than with Methanol-to-Gasoline with 20%(V/V) ethanol (MtG-E20), despite the lower alcohol volume fraction. In contrast, Methanol-to-Gasoline with 15%(V/V) 2-butanol (MtG-2Bu15) showed no improvement. POSYN enabled a significant efficiency advantage over RON95 E10 because of its high knock resistance, however, achieved the same maximum engine load because of the reduced octane sensitivity. The variation of the relative air/fuel ratio at an engine speed of 2500 rpm and an engine load of 16 bar net indicated mean effective pressure confirmed these findings. The highest net indicated efficiency of 42.4% was achieved with POSYN at a relative air/fuel ratio of 1.6. The lean limit could not be increased with the synthetic fuels and alcohol blends albeit with an improved combustion stability.
Wouters, Christian, Lehrheuer, Bastian, Pischinger, Stefan, Seifert, Peter, Raabe, Toni, Kolbeck, Michael, Rausch, Benjamin, Menger, Lars, Casal Kulzer, André
Effects of Octane Number and Sensitivity on Combustion of Jet Ignition Engine2022-01-04353/29/2022
Octane number (ON) and octane sensitivity (S), the fuel anti-knock indices, are critical for the design of advanced jet ignition engines. In this study, ten fuels with different research octane number (RON) and varying S were formulated based on ethanol reference fuels (ERFs) to investigate the effect of S on combustion of jet ignition engine. To fully understand S effects, the combustion characteristics under EGR dilution and lean burn were further investigated. The results indicated that increasing S resulted in higher reactivity with shorter ignition delay and combustion duration. The increase of reactivity led to heavier knocking intensity. The competition between the flame speed and the reactivity of the mixture determined the auto-ignition fraction of mixture and the knocking onset crank angle as S varied. Medium S (S=3) was helpful to improve the combustion speed, reduce the auto-ignition fraction of mixture and retard the knocking onset crank angle. For high RON (RON=100) and medium RON (RON=93) fuel, medium S (S=3) could better balance the combustion and emission, achieving higher indicated thermal efficiency (ITE). Whereas, low S (S=0) was more favorable for low RON fuel (RON=85). For the same MON fuel, increasing S reduced the knocking intensity and benefited ITE. The increase of reactivity remained for higher S fuel under EGR dilution and lean burn conditions. More stable engine operation was observed for high S fuel (S>7) allowing for higher dilution tolerance and promising to achieve higher ITE. Through active jet ignition under lean burn, the combustion was improved with lower knocking intensity. Benefited from faster combustion speed and lower combustion temperature, higher ITE was achieved by high S fuel under lean burn.
Zhao, Ziqing, Cai, Kaiyuan, Wang, Wei, Li, Yanfei
Increasing the Effective AKI of Fuels Using Port Water Injection (Part II)2022-01-04343/29/2022
This is the second part of a study on using port water injection to quantifiably enhance the knock performance of fuels. In the United States, the metric used to quantify the anti-knock performance of fuels is Anti Knock Index (AKI), which is the average of Research Octane Number (RON) and Motor Octane Number (MON). Fuels with higher AKI are expected to have better knock mitigating properties, enabling the engine to run closer to Maximum Brake Torque (MBT) spark timing in the knock limited region. The work done in part I of the study related increased knock tolerance due to water injection to increased fuel AKI, thus establishing an ‘effective AKI’ due to water injection. This paper builds upon the work done in part I of the study by repeating a part of the test matrix with Primary Reference Fuels (PRFs), with iso-octane (PRF100) as the reference fuel and lower PRFs used to match its performance with the help of port water injection. Additionally, the unburned gas pressure-temperature trajectories for varying loads were analyzed to better understand the underlying physics of port water injection in engines. Finally, a comparison was made between the amount of water and excess fuel required to gain a similar increase in effective AKI.
Gopujkar, Siddharth, Worm, Jeremy, Barros, Sam, Bonfochi Vinhaes, Vinicius, Hansley, William
Effect of Substituted Phenol Fuel Additives on Ignition Delay of a Toluene Reference Fuel2022-01-05163/29/2022
Aromatics have long been used in pump-grade gasoline to inhibit engine knock and enhance a fuel’s octane number, therefore this study focuses on how the addition of aromatics at 2% by mole affects the ignition characteristics of a Toluene Reference Fuel (TRF). The additives investigated in this study are the substituted phenols p-cresol and 2,6-xylenol. In addition to fuel composition, exhaust gas recirculation dilution can be used to lower the combustion temperature and consequently lengthen the ignition delay time of a given fuel-air mixture. This study replicated exhaust gas recirculation dilution by using N2, as it was inert and did not interfere with reactions between the fuel and oxidizer. Determination of whether the similar structures of p-cresol and 2,6-xylenol result in different autoignition inhibiting characteristics was performed on a rapid compression machine. Each fuel mixture was tested over a range of engine-relevant compressed temperatures, equivalence ratios, and N2 dilution ratios at 20 bar compressed pressure, to see how the ignition delay time varied with each condition. The measurements of the p-cresol and 2,6-xylenol mixtures were then compared to the toluene reference fuel, and it was found that the additives had the strongest lengthening effect on ignition delay time for stoichiometric and lean mixtures at the lowest temperatures investigated. Additionally, it was found that increasing the N2 dilution in a stoichiometric fuel-air mixture was associated with increasingly long ignition delay times.
Trombley, Grace, Wadkar, Chaitanya, Duva, Berk Can, Toulson, Elisa
Adaptation and Engine Validation of an FTIR Exhaust Gas Analysis Method for C1-Based Potential GHG-Neutral Synthetic Fuels/Gasoline-Blends Containing Dimethyl Carbonate and Methyl Formate2022-01-05693/29/2022
The European Commission has released strict emission regulations for passenger cars in the past decade in order to improve air quality in cities and limit harmful emission exposure to humans. In the near future, even stricter regulations containing more realistic/demanding driving scenarios and covering more exhaust gas components are expected to be released. Passenger cars fueled with gasoline are one contributor to unhealthy air conditions, due to the fact that gasoline engines emit harmful air pollutants. One option to minimize harmful emissions would be to utilize specifically tailored, low emission synthetic fuels or fuel blends in internal combustion engines. Methyl formate and dimethyl carbonate are two promising candidates to replace or substitute gasoline, which in previous studies have proven to significantly decrease harmful pollutants. This is especially in regard to particle emissions, while offering beneficial properties for SI combustion, such as high octane rating and high laminar flame speed. FTIR-analyzers are a viable option for measuring future-restricted emissions, such as methane, ammonia, and formaldehyde, simultaneously with currently restricted emissions like NOx and CO. Such analyzers provide deep insight into gaseous emissions of an engine. However, the underlying method of evaluation must be adapted to the fuel and exhaust components to provide reliable, realistic, and reproducible data. This paper provides an insight of how a currently available method of FTIR spectra analysis for gasoline can be adapted to synthetic fuels containing Dimethyl carbonate (DMC) and Methyl Formate (MeFo). To validate the new method for these two components, several synthetic fuels and blends with gasoline will be analyzed. Exhaust gases of a single cylinder research engine fueled with 100 vol% DMC, 100 vol% MeFo, 65 vol% DMC and 35 vol% MeFo, five different DMC-gasoline blends and one MeFo-gasoline blend is used. Additionally, two mixtures of alkylate gasoline with MeFo and one methanol-MeFo mixture is shown. Alkylate gasoline is chosen due to its reduced PN-emissions and chemical properties similar to synthetically produced gasoline.
Kraus, Christoph, Jakubec, Philipp, Girhe, Sanket, Fellner, Felix, Härtl, Martin, Jaensch, Malte, Wachtmeister, Georg, Pitsch, Heinz
Benefits of Octane-On-Demand in an E10-Gasoline Engine Vehicle Using an On-Board Fuel Separator2022-01-04243/29/2022
Knock in gasoline engines at higher loads is a significant constraint on torque and efficiency. The anti-knock property of a fuel is closely related to its research octane number (RON). Ethanol has superior RON compared to gasoline and thus has been commonly used to blend with gasoline in commercial gasolines. However, as the RON of a fuel is constant, it has not been used as needed in a vehicle. To wisely use the RON, an On-Board Separation (OBS) unit that separates commercial gasoline with ethanol content into high-octane fuel with high ethanol fraction and a lower octane remainder has been developed. Then an onboard Octane-on-demand (OOD) concept uses both fuels in varying proportion to provide to the engine a fuel blend with just enough RON to meet the ever changing octane requirement that depends on driving pattern. In this work, the authors assessed the OOD concept on a state-of-art high-efficiency SI engine in three tasks: (1) Comparison of performance characteristics of an up-to-date reference engine coupled with cylinder deactivation (CDA) system, with a similar OOD engine. (2) Study of the OOD engine performance at vehicle level. This involves interaction between the time-dependent onboard fuel separation process and fuel consumption under different driving cycles, such as FTP75 and US06. (3) Potential of the OOD concept for engine downsizing with the needed boosting to maintain maximum torque. It was found that overall mid-to-high load engine efficiency is improved significantly with the OOD engine. However, the improvement in the CDA operating region is small due to the higher combined pumping and friction losses at higher load region where knock occurs. At the vehicle level, the performance of OOD engine is dependent on the control strategy. With appropriate spark control strategy, the efficiency improvement with OOD engine is between 1% and 1.5%, depending on the aggressiveness of the driving pattern. The OOD concept is an attractive approach to increase efficiency of downsized engine. However, this requires the ethanol content in the pump fuel be significantly higher than currently typical 10% levels.
Chen, Yu, Kasseris, Emmanuel, Heywood, John, Han, Donghee, Kim, Jaeheun, Lee, Kwanhee, Kang, Hyunjin, Zhou, Jinsheng, Mizuno, Kazuhiko, Seitz, Scott, Kim, Seongju, Min, Seungbae, Peters, Nathan, Subramanyam, Sai Krishna P., Bunce, Michael
Autoignition and Sooting Characteristics of Iso -Octane and Ethanol in an Optical Rapid Compression Machine2022-01-04193/29/2022
With the introduction of EV technology into the light-duty vehicle market, the demand for gasoline in conventional spark ignition engines is projected to decline in the coming decades. Therefore, researchers have been investigating the use of gasoline and other light fuels in heavy-duty engine applications. In heavy-duty engines, the combustion mode will likely be non-premixed, mixing-controlled combustion, where the rate of combustion is determined by the fuel-air mixing process. This creates a range of mixture conditions inside the engine cylinder at every instance in time. The goal of this research is to experimentally quantify the sooting behaviors of light fuels under a range of compression ignition engine mixture conditions (i.e., a range of equivalence ratios). Accordingly, an optical rapid compression machine (RCM) was used to compress charges of iso-octane and ethanol to autoignition conditions, which varied between a fuel-air equivalence ratio of 1.6 to 2.3 and 1.9 to 2.5, respectively. This equivalence ratio span showed a transition from non-sooting conditions to a limit where the burned mixture after combustion became optically thick, as measured by a line-of-sight laser extinction diagnostic. Data from the laser extinction diagnostic indicated that pure iso-octane begins to form measurable soot at an equivalence ratio of ~1.85, whereas pure ethanol begins forming soot at an equivalence ratio of ~2.2. If the data are compared on the basis of an oxygenated equivalence ratio, which accounts for fuel-bound oxygen, both fuels begin to form soot at a similar oxygenated equivalence ratio of ~1.85.
Kempf, John, Dempsey, Adam, Allen, Casey
A Prediction Model of RON Loss Based on Neural Network2022-01-01623/29/2022
The RON(Research Octane Number) is the most important indicator of motor petrol, and the petrol refining process is one of the important links in petrol production. However, RON is often lost during petrol refining and RON Loss means the value of RON lost during petrol refining. The prediction of the RON loss of petrol during the refining process is helpful to the improvement of petrol refining process and the processing of petrol. The traditional RON prediction method relied on physical and chemical properties, and did not fully consider the high nonlinearity and strong coupling relationship of the petrol refining process. There is a lack of data-driven RON loss models. This paper studies the construction of the RON loss model in the petrol refining process. The main innovation is to use frequency statistics to summarize the operating range of data variables and preprocess the dataset, and use the variance selection method to filter out some invalid variables, then use the multi-dimensional association analysis to select 27 main operating variables in the next step. Finally, a neural network is used to establish an RON loss prediction model, and the prediction accuracy is 85.22%.
Zhang, Sumin, Yang, Gang, Li, Shuai, Li, Wenju
Integration and Validation of a Quasi-Dimensional Modelling Methodology and Application to Light-Duty and Heavy-Duty Methanol-Fueled Spark-Ignited Engines2022-01-03853/29/2022
To speed up the development of the next-generation combustion engines with renewable fuels, the importance of reliable and robust simulations cannot be overemphasized. Compared to gasoline, methanol is a promising fuel for spark-ignited engines due to its higher research octane number to resist auto-ignition, higher flame speed for faster combustion and higher heat of vaporization for intake charge cooling. These advantageous properties all contribute to higher thermal efficiency and lower knock tendency, and they need to be well-captured in the simulation environment in order to generate accurate predictions. In this paper, the sub-models which estimate the burning velocities and ignition delay of methanol are revisited. These building blocks are implemented and integrated in a quasi-dimensional simulation environment to predict the combustion behavior, which are subsequently validated against test data measured on both light-duty and heavy-duty engines. The light-duty application is represented by a spark advance sweep on a CFR engine with compression ratios ranging from 9 to 11 and lambda ranging from 0.7 to 1.3. The heavy-duty application is represented by a sweep of the indicated mean effective pressure on a Scania D12 engine from 13 to 26 bar with boost levels from 50 mbar to 1.5 bar and lambda from 1 to 1.8. The calibration results of the model for both applications are compared and discussed. The simulation results show that the current methodology works well with the light-duty application but extra work on the burning velocity sub-model is required to better capture the combustion behavior in heavy-duty applications.
Pu, Yi-Hao, Verhelst, Sebastian
Comparative analysis of the internal combustion engine block vibration with gasoline and ethanol fuel2021-36-00102/4/2022
Ethanol and gasoline are widely used with fuels in Otto cycle engines. These fuels have different heating power and octane number and the engine behaves differently depending on the type of fuel used. The objective of this study is to measure, compare and investigate the factors that affect the block vibration of an internal combustion engine as a function of the fuel used ethanol or gasoline. The experiment consisted of instrumenting the side of the engine block with an accelerometer to measure the level of vibration intensity of the engine running on a bench dynamometer varying engine speed and load conditions. The results showed that the engine vibration level increases with the increase in engine speed and load. The highest level of vibration was achieved in the region of maximum torque and maximum pressure combustion. The combustion process is mainly responsible for the highest level of vibration achieved with ethanol. In all operating conditions the vibration level of the engine block was higher as ethanol. On average, the longitudinal, vertical and transverse engine vibration was 3%, 31% and 56% higher in the engine running on ethanol compared to the engine using gasoline. This research is important because it correlates the vibration level of the block of an internal combustion engine as an engine combustion process fueled with ethanol and gasoline.
Santana, Claudio Marcio, Barros, Jose Eduardo Mautone, de Almeida Junior, Helder Alves
Determination of Octane Index and K-Factor in a 2.0L, Four-Cylinder Turbocharged SI Engine Using the Primary Reference Fuel Method—Part II2022-01-50061/24/2022
This is the second part of a two-phase study revolving around the determination of fuel K-factor for different fuels in a 2.0L, 4-cylinder, direct-injected, turbocharged spark-ignition (SI) engine for different engine speeds and loads. Prior studies relating to K-factor claim that K depends only on the engine’s combustion system and operating condition, but Phase 1 of this study detected contrary results. Experimental determination of K at multiple test points showed the K value was different for the Environmental Protection Agency (EPA) certification Tier 2 and Tier 3 regular fuels. That study also found strong correlations of the K value with macroscopic parameters (e.g., speed, load, and combustion phasing) and end gas conditions, irrespective of the fuel. This second phase of the study showed that the effect of variation in day-to-day conditions on the K-factor is negligible and that K-factor stays the same with changes in intake air temperature (IAT) for a specific speed-load condition.
Gopujkar, Siddharth B., Worm, Jeremy, Davis, Richard S.
Describing the Auto-Ignition Quality in Small, Air Cooled, Two Stroke Engines2022-32-00631/9/2022
Auto-ignition quality is one of the most important properties in gasoline. Auto-ignition quality is today described by the Motor Octane Number (MON) and the Research Octane Number (RON). For modern, light duty, gasoline engines it has been quite well established that RON is the most accurate number. However, no study has been performed on hand held forest and garden products, such as chainsaws. Is the auto-ignition quality best described in the same way for these engines as for light duty engines? In this paper, a matrix of six different fuels with different combinations of MON and RON values were tested on a Husqvarna 550 XP Mark II, a modern air cooled, sequential stratified scavenging 2-stroke chainsaw engine. Ignition timing sweeps were performed and knock limited spark advance (KLSA) were calculated. Then the data has been analyzed with a multi-variate analysis of KLSA against both MON and RON to try to determine how MON and RON should be combined to best describe the anti-knock quality on this specific engine. The results show that neither MON nor RON describes the anti-knock quality well on this product. The AKI (the average of RON and MON) described the anti-knock quality best of the conventionally recognized anti-knock quality measurements. From the multivariate analysis the K-value was determined to be 0,59. Using a fuel with a more ideal combination of MON and RON on this type of products without knock control can limit the maximum cylinder pressure and cylinder top temperature. This is likely to extend the life time of the forest and garden equipment significantly. Small engine gasoline fuel, also known as alkylate gasoline, has a good combination of RON and MON that makes it outperform other market fuels from an Anti-knock quality perspective on the tested engine. At the same time small engine gasoline has other benefits, such as less health hazardous exhaust emissions, that can improve the work environment for loggers. This tailor made forest and garden fuel remain mysteriously anonymous outside of Europe.
Risberg, Per, Elm, Thomas, Bergman, Mikael, Hellquist, Fredrik, Karvo, Anna, Tripathi, Rupali
Effect of Ethanol-Gasoline Blends on Adsorption/Desorption Process in SI Engine2021-01-11849/21/2021
Ethanol is regarded as a potential alternative fuel for combustion engine as it provides lower exhaust emissions, higher efficiency and higher octane rating. However, the solubility of ethanol in oil can effect lubricant quality. The impact of ethanol-blend gasoline on lubricants is a matter of concern that must be addressed. With this in mind, the current study investigates the effect of blending ethanol with gasoline on the oil layer adsorption/desorption mechanism. The blends used for the study are E0, E5, E10, and E15. The study is carried out with the help of a mathematical model that predicts the fuel adsorbed/desorbed in the oil layer of an engine. The mathematical model predictions are compared to experimental results obtained on a single-cylinder gasoline engine. Fuel adsorbed in the oil layer ranges from 0.46% for E0 fuel to 0.35% for E15 fuel. Similarly, the desorbed fuel ranges from 0.45% to 0.29% as the ethanol fraction increases from 0% to 15%. Despite the fact that the amount of fuel adsorbed/desorbed in the oil layer decreases as the ethanol fraction increases, the amount of fuel stored in the oil layer (i.e., the difference between adsorbed and desorbed fuel) increases from 0.01 percent to 0.06 percent which can significantly degrade the lubricant quality.
Kushwaha, Garima, Saraswati, Samir, Paul PhD, Bireswar
Fuel Effects on Advanced Compression Ignition Load Limits2021-01-11729/21/2021
In order to maximize the efficiency of light-duty gasoline engines, the Co-Optimization of Fuels and Engines (Co-Optima) initiative from the U.S. Department of Energy is investigating multi-mode combustion strategies. Multi-mode combustion can be describe as using conventional spark-ignited combustion at high loads, and at the part-load operating conditions, various advanced compression ignition (ACI) strategies are being investigated to increase efficiency. Of particular interest to the Co-Optima initiative is the extent to which optimal fuel properties and compositions can enable higher efficiency ACI combustion over larger portions of the operating map. Extending the speed-load range of these ACI modes can enable greater part-load efficiency improvements for multi-mode combustion strategies. In this manuscript, we investigate fuel effects for six different fuels, including four with a research octane number (RON) of 98 and differing fuel chemistries, iso-octane, and a market representative E10 fuel, on the load limits for two different ACI strategies: spark-assisted compression ignition (SACI) and partial fuel stratification-gasoline compression ignition (PFS-GCI) operation. Experimental results show that limits to intake boosting limit high load operation for most fuels, but high smoke emissions for high particulate matter index (PMI) fuels under SACI conditions could also be a limitation. Contrastingly, low load is limited by combustion efficiency, but these effects have more pronounced variation with fuel chemistry for PFS-GCI than with SACI. Additional, distinct effects affecting autoignition timing and peak heat release at higher speeds were identified for fuels having different low temperature heat release (LTHR) propensities for both ACI modes.
Powell, Tommy, Szybist, James
Fuel Stratification Effects on Gasoline Compression Ignition with a Regular-Grade Gasoline on a Single-Cylinder Medium-Duty Diesel Engine at Low Load2021-01-11739/21/2021
Prior research studies have investigated a wide variety of gasoline compression ignition (GCI) injection strategies and the resulting fuel stratification levels to maintain control over the combustion phasing, duration, and heat release rate. Previous GCI research at the US Department of Energy’s Oak Ridge National Laboratory has shown that for a combustion mode with a low degree of fuel stratification, called “partial fuel stratification” (PFS), gasoline range fuels with anti-knock index values in the range of regular-grade gasoline (~87 anti-knock index or higher) provides very little controllability over the timing of combustion without significant boost pressures. On the contrary, heavy fuel stratification (HFS) provides control over combustion phasing but has challenges achieving low temperature combustion operation, which has the benefits of low NOX and soot emissions, because of the air handling burdens associated with the required high exhaust gas recirculation rates. This work investigates HFS and PFS combustion, efficiency, and emissions performance on a single-cylinder, medium-duty engine with a regular-grade gasoline (91 research octane number) at 1,200 rpm, 4.3 bar, and 3.0 nominal gross indicated mean effective pressure operating points with boost levels similar to those in a medium-duty diesel application. Authority of combustion phasing with main injection timing sweeps for HFS and second injection timing sweeps and fuel split sweeps for PFS are shown. In addition, this work is discussed in the context of previous findings with a light-duty diesel platform, and next steps and future direction for this work are presented1.
Curran, Scott, Szybist, James, Kaul, Brian, Easter, Jordan, Sluder, Scott
Impact of CO 2 Dilution on Ignition Delay Times of Full Blend Gasolines in a Rapid Compression Machine2021-01-11999/21/2021
Autoignition delay times of two full blend gasoline fuels (high and low RON) were explored in a rapid compression machine. CO2 dilution by mass was introduced at 0%, 15%, and 30% levels with the O2:N2 mole ratio fixed at 1:3.76. This dilution strategy is used to represent exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines by using CO2 as a surrogate for major EGR constituents(N2, CO2, H2O). Experiments were conducted over the temperature range of 650K-900K and at 10 bar and 20 bar compressed pressure conditions for equivalence ratios of (Φ =) 0.6-1.3. The full blend fuels were admitted directly into the combustion chamber for mixture preparation using the direct test chamber (DTC) approach. CO2 addition retarded the autoignition times for the fuels studied here. The retarding effect of the CO2 dilution was more pronounced in the NTC region when compared to the lower and higher temperature range. The effect of dilution was more pronounced for the higher RON fuel in comparison to the lower RON fuel. With CO2 dilution, ignition delay times of the low RON fuel matched the undiluted high RON fuel delay times showcasing octane relaxation potential. The ignition delay times of the gasoline fuels were compared with that of iso-octane, a major component in gasoline surrogates, at both diluted and undiluted conditions. The CO2 dilution did not affect the ignition delay curve of the fuels or iso-octane but rather shifted it horizontally, hence no significant chemical reactivity due to CO2 dilution was observed in this study.
Chinnathambi, Prasanna, Wadkar, Chaitanya, Gudiyella, Soumya, Estefanous, Fadi, Toulson, Elisa
Auto-ignition and Anti-Knock Evaluation of Dicyclopentadiene-PRF and TPRF Blends2021-01-11609/21/2021
The increasing demand for high-octane fuels is pushing the combustion research towards investigating new potential fuels and octane boosters. In addition to their high-octane, those additives should be environmentally friendly. In this study, the anti-knock properties of Dicyclopentadiene (DCPD) as an additive to primary reference fuels (PRF) and toluene primary reference fuels (TPRF) have been investigated. The Research octane number (RON) and Motor octane number (MON) were measured using Cooperative Fuels Research (CFR) engine for four different fuel blends; PRF 60 + 10% DCPD, PRF 60 + 20% DCPD, PRF 70 + 10% DCPD and TPRF 70 + 10% DCPD. In addition, homogenous charge compression ignition (HCCI) was also performed using the CFR engine to show the effect of DCPD on suppressing low temperature chemistry of reference fuels. Moreover, the ignition delay times of these mixtures were measured in the rapid compression machine (RCM) at 20 bar and stoichiometric mixtures over a temperature range [700-1000 K]. Also, ignition quality tester (IQT) was used to determine the effect of DCPD addition to iso-octane. Generally, DCPD showed superior anti-knock quality, which is attributed to its combustion chemistry.
Al-Khodaier, Mohannad
On the Relevance of Octane Sensitivity in Heavily Downsized Spark-Ignited Engines2021-24-00549/5/2021
Over the years, spark-ignition engine operation has changed significantly, driven by many factors including changes in operating conditions. The variation in operating conditions impacts the state of the end-gas, and therefore, its auto-ignition. This can be quantified in terms of K-factor, which weighs the relative contribution of Research Octane Number (RON) and Motor Octane Number (MON) to knocking tendency at any operating condition. The current study investigates the fuel requirements when operating an engine at increasing intake air pressures. A model engine was operated at varying intake air pressure in GT-Power software, from naturally aspirated intake air to heavily boosted intake air pressure of 4 bar absolute. The pressure-temperature information from the GT-Power model was used to calculate ignition delay times of the unburnt end-gas composed of a sensitive and a non-sensitive fuel in ChemKin software. The results show that high octane sensitivity is desired at negative K values (operating at high intake air pressures). In contrast, zero octane sensitivity fuel performed best at low load operation (positive K). Interestingly, the maximum benefit for using a sensitive fuel was achieved at an intake air pressure of 1.75 bar with diminishing returns at higher intake air pressure for 1000 rpm and at lower intake pressures, as engine speed increased. The pressure effect on auto-ignition tendency was also investigated over existing HCCI data. The auto-ignition tendency was found to be sensitive to octane index in a region of low K value (K~0). This region lies in the negative temperature coefficient (NTC) region, where Primary Reference Fuels (PRFs) shown an increased sensitivity to pressure variation.
Singh, Eshan, Mohammed, Abdulrahman, Gorbatenko, Inna, Sarathy, Mani
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