Browse Topic: Fuel additives
In the rapidly changing scenario of the energy transition, data-driven tools for kinetic mechanism development and testing can greatly support the evaluation of the combustion properties of new potential e-fuels. Despite the effectiveness of kinetic mechanism generation and optimization procedures and the increased availability of experimental data, integrated methodologies combining data analysis, kinetic simulations, chemical lumping, and kinetic mechanism optimization are still lacking. This paper presents an integrated workflow that combines recently developed automated tools for kinetic mechanism development and testing, from data collection to kinetic model reduction and optimization. The proposed methodology is applied to build a consistent, efficient, and well-performing kinetic mechanism for the combustion of oxymethylene ethers (OMEs), which are promising synthetic e-fuels for transportation. In fact, OMEs are easily mixed with conventional fuels and share similar ignition propensity, and are therefore potential drop-in fuels. Additionally, their oxygenated nature significantly reduces soot emissions. The proposed workflow extends our recently developed kinetic mechanism for OME1 (dimethoxymethane – DMM) to OME2-4: the model is derived from state-of-the-art detailed literature mechanisms, updated according to a reaction class-based approach, and simplified according to chemical lumping. Then, the model is reduced to two different skeletal versions using DRGEP method. An extensive database of ~80 datasets for kinetic mechanism testing is collected, covering different reactor types and experimental conditions. The selected datasets are uploaded to SciExpeM, a recently developed data ecosystem that allows automated kinetic mechanism performance evaluation through a multi-index approach. The performance obtained from SciExpeM shows that the lumped mechanism reproduces well the selected experimental data, and both skeletal mechanisms, well-suited to CFD and engine simulations, show equally good performance. Some minor model deficiencies identified for OME2 and OME3 are finally recovered via data-driven kinetic modeling optimization, which relies on the same multi-index approach adopted in SciExpeM for the kinetic model evaluation.
Diesel engines operated at high altitudes would experience performance degradation due to the fuel-air amount mismatch, resulting in combustion deterioration. Technologies that supplement oxygen concentration, such as intake oxygen enrichment, turbocharging and the addition of oxygenated fuel additives, can help restore performance at high altitudes, but each has its own limitations Operating diesel engines at high altitudes still generates extremely lean fuel-air mixtures, making the improved utilization of excess air the most economically efficient approach to optimize engine performance under such conditions. The objective of this paper is to investigate the effects of injector nozzle-hole numbers on diesel engines operated at high altitudes, a topic that has been limitedly discussed in existing literature, with the aim of enhancing understanding regarding the potential of this cost-effective approach and aiding in the design of a cooperative approach between oxygen concentration supplementation techniques and better oxygen utilization techniques, ultimately optimizing engine performance at high altitudes. The results suggest that increasing the number of nozzle-holes enhances fuel-air mixing, leading to improved combustion quality and enhancing the engine’s adaptability to altitude. However, at extremely high altitudes, such as altitudes exceeding 3000 meters, configurations with a larger number of nozzle-holes still exhibit high concentrations of incomplete combustion products, such as soot emissions, in the exhaust. This reduced combustion efficiency is mainly attributed to the longer spray penetration length at high altitudes, which causes intensified spray impingement on the cavity wall, subsequently resulting in inefficient combustion of the fuel flowing into the squish zone during spray impingement. This inefficiency may be mitigated by optimizing the shape of the combustion chamber. It is worth noting that increasing the number of nozzle-holes can also lead to a higher pressure rise rate. Considering that high altitude operations already result in a higher pressure rise rate, further increasing the nozzle-hole number may exceed the allowable threshold and increase the likelihood of engine component failure. Consequently, the strength of engine components becomes a limiting factor when attempting to increase the number of nozzle-holes for improved engine altitude adaptation.
Thermal control coatings, i.e. coatings with different visible versus infrared emission, have been used by NASA on the Orbiter and Hubble Telescope to reflect sunlight, while allowing heat rejection via infrared emission. However, these coatings absorb at least 6 percent of the Sun’s irradiant power, limiting the minimum temperature that can be reached to about 200 K. NASA needs better solar reflectors to keep cryogenic fuel and oxidizers cold enough to be maintained passively in deep space for future missions.
Engine design and selection of fuels for automotive applications are required to minimize noise and exhaust emissions without compromising fuel economy. The knocking combustion investigation is essential as it directly affects the performance and durability as well as the thermal efficiency of the engine. Several fuel additives were suggested in the previous studies to mitigate the knocking combustion in spark ignition (SI) engines. The present study reviews the effect of antiknock fuel additives such as ethanol, methanol, prenol, n-butanol, furan mixtures, etc., on knocking behavior in SI engines. Additionally, this paper aims to present a systematic review of the studies conducted to investigate the effect of EGR on the knocking in SI engines. The EGR is often considered an effective means to suppress knocking in SI engines. The thermal effect of EGR in controlling the knocking is well known as EGR affects the temperature and pressure history of the combustion chamber. The main constituting components of EGR are CO2, H2O, NO, and N2. It is found from the published studies that CO2 has a strong chemical effect on knocking through a chemical reaction between CO2 and hydrogen. CO2 also plays a significant role in the suppression of the temperature rise. The CO2 has a more substantial effect than H2O on laminar burning velocity. Nitric oxide (NO) present in the EGR also affects autoignition and knocking. It is demonstrated that knocking can be suppressed with NO addition, but the fuel must have a strong negative temperature coefficient in some specific conditions. Based on the literature review, future research directions are also proposed for further studies.
Gasoline Direct Injection (GDI) fuel injectors are fouled when carbon deposits build-up on the injector tip, impeding fuel droplet atomization and dispersion. These issues, if left untreated, can lead to losses in engine power and fuel economy, as well as increased emissions of particulate matter (PM). Bottled aftermarket gasoline detergents are commonly used to remove deposits and restore injector performance. A performance analysis of three classes of bottled gasoline additives was performed, focusing on products that do not contain nitrogen-based detergents; products containing nitrogen-based detergents; and a new class of gasoline detergent formulations designed specifically for GDI injector fouling. Analyses completed included additive chemical analysis to confirm the presence of nitrogen-based gasoline detergents in the bottled product; engine testing to establish injector clean-up performance quantified through injected fuel spray volume as well as visual inspection of reduced injector tip deposits; and particulate matter mass measurements to assess the emissions impacts due to deposit build-up. The resultant analyses show nitrogen-based gasoline detergents are most effective in reducing injector fouling. Further, a new formulation, designed specifically to reduce injector fouling in GDI engines results in the highest level of injector cleanliness and reductions in PM emissions.
Butanol is a potential alternative fuel for diesel in compression ignition (CI) engines. Many of the physico-chemical properties of butanol such as low carbon-to-hydrogen (C/H) ratio compared to diesel, higher heating value, lower heat of vaporization and suitable density-viscosity values compared to ethanol and methanol makes it suitable as an alternative fuel. However, poor cetane number and miscibility are the limitations associated with butanol. The use of fuel additives as ignition improver could be beneficial in overcoming the issues associated with alcohols. In this work, an experimental investigation in a twin-cylinder CI engine was carried out to assess the effect of doped cetane improving additives (Diethyl ether (DEE), Diglyme (DEGME) and Ethyl diglyme (DEGEE)) for diesel-butanol blend (B15). Cylinder pressure trace, heat release rate (HRR), location of maximum in-cylinder pressure (Pmax) and maximum rate of heat release (HRRmax), engine performance (brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC)) and gaseous emissions (oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2) and total volatile organic compounds (VOCs)) for blends of diesel and butanol (15% v/v) were measured and evaluated to determine the effect of these doped additives. B15 showed elevated cylinder pressure (~9% higher than diesel Pmax) and higher HRRmax (~9.3% higher than diesel). Higher BTE and lowest BSFC was recorded for B15 doped with DEE (B15+DEE) with lowest CO2, NOx and VOCs emissions among tested conditions.
This study presents the developmental work of two reduced kinetic models, namely, methyl-cyclo-hexane (MCH) and pentanol. MCH is the representative of the cyclo-alkane component for diesel. Pentanol is used as a fuel additive to aid in emission reduction. The final 86-species MCH model and the final 55-species pentanol model are about 90% smaller than their respective detailed counterparts. Upon extensive validation exercises in zero-dimensional (0-D) kinetic simulations, the MCH model was integrated with the formerly derived models for linear (n-hexadecane) and branched (2,2,4,4,6,8,8-heptamethylnonane) alkanes to form a 144-species kinetic model, namely, D_144. The “reduced-prior-to-combination” approach was adopted in merging the fuel constituents. The D_144 model can be used as a surrogate model for diesel in numerical computational fluid dynamics (CFD) modelling. Successively, a 162-species model for diesel and alcohol mixtures, namely, DA_162, was formulated by integrating the alcohol chemistries of the pentanol model with the D_144 model. It was then applied in spray combustion simulations to evaluate the effects of the alcohol additive on the combustion and emission performances of diesel fuel under diesel-engine-like conditions. The results obtained showed that blending of alcohol additives with diesel has successfully reduced soot formation. The DA_162 model can potentially be used as a surrogate model in further investigation studies involving alcohol-diesel-fuelled engines.
The transport of fuel-borne additives into the engine oil is a critical factor for the efficacy with which the additive functionality can be imparted on the engine. This paper describes the combination of Laser Induced Fluorescence (LIF) and Liquid Chromatography (LC) to determine the real-time additive concentrations and transfer ratios in a spark-ignition, 2-liter GM LHU engine. The current research used a continuous sample circuit from the engine sump which passed through an integrating cavity flow cell to enhance the LIF signal. In the absence of a fluorescence signature of any of the native additive species, a suitable fluorescing dye was selected to simulate the additive. After establishing rigorous calibration curves, LC was employed as a referee method to do a direct comparison with the LIF determined dye concentrations. The impact of the oil age and fuel dilution on the dye LIF signal was aggregated to a scaling factor which was a function of the relative absorption (RA) of the samples. In addition to the continuous LIF measurement, regular samples were used for RA determination and LC analyses. Based on the dye concentrations, transport ratios were determined which revealed the percentage of dye that accumulated in the engine oil over time. Good agreement was found between the transport ratios for the dye by the two methods.
The U.S. Environmental Protection Agency (EPA) certifies gasoline deposit control additives for intake valve deposit (IVD) control utilizing ASTM D5500, a vehicle test using a1985 BMW 318i. Concerns with the age of the test fleet, its relevance in the market today, and the availability of replacement parts led the American Chemistry Council’s (ACC) Fuel Additive Task Group (FATG) to begin a program to develop a replacement. General Motors suggested using a 2.4L LE9 test engine mounted on a dynamometer and committed to support the engine until 2030. Southwest Research Institute (SwRI®) was contracted to run the development program in four Phases. In Phase I, the engine test stand was configured, and a test fuel selected. In Phase II, a series of tests were run to identify a cycle that would build an acceptable level of deposits on un-additized fuel. In Phase III, the resultant test cycle was examined for repeatability. In Phases IVa and IVb, two discrimination matrices evaluated the response of additives on IVD levels. The results of Phase IVa indicated the EPA 65thpercentilefuel and test procedure combination did not compare with historical BMW results or replicate additive discrimination. The results of Phase IVb, using a TOP TIER™ certification fuel, showed a representative additive response in the LE9. ACC FATG considers the initial test development complete, but continued evaluation of the fuel, hardware, and test cycle will be required. With continued development in a Coordinating Research Council program, ACC FATG anticipates that the 9 2.4L IVD test can be standardized as an ASTM test method, and used as an alternate or replacement for the ASTM D5500 in both EPA and California Air Resources Board Reformulated Gasoline regulations. This would also position the 2.4L IVD test to become a replacement for the ASTM D6201 IVD test.
Global warming due to exhaust emissions, rapid depletion of crude oil, and strict carbon control legislation has forced researchers to search biofuels as substitute for petroleum diesel fuels. Biodiesel is a renewable and oxygenated fuel. It is free from sulfur, non-toxic and a biodegradable. The different non-edible vegetable oils such as Algae, Karanja and Jatropha could be used to produce biodiesel. Biodiesel is a green fuel with an exception that it emits 15-20% more NOx as compared to diesel fuel. The emissions of nanoparticles are more hazardous to human health. The nanoparticles emission of biodiesel must be measured according to the new strict regulations. The engine performance and the lower emission characteristics, except for NOx emission, for Algae, Karanja and Jatropha oil biodiesels are similar to those of diesel fuel. Present study has investigated the performance, combustion and emissions, including nanoparticle emissions, for Algae, Karanja and Jatropha oil biodiesel using CeO2 as fuel additive in military heavy duty, 582kW, CIDI engine. In research investigations, engine power output with Algae, Karanja, and Jatropha biodiesel fuel was found to be marginally lower as compared to diesel fuel. Biodiesel fuels blended with Cerium oxide as fuel additive, resulted in lower engine exhaust emissions with 22-28% reduction in NOx emissions as well as lower nanoparticle emissions.
Sustainable fuels can help to decrease carbon dioxide emissions in road transportation compared to standard fossil fuels. The most common sustainable fuels used today in heavy-duty applications are biodiesel and hydrogenated vegetable oil (HVO). Biodiesel and HVO are known as drop-in fuels since they are fuels that can be blended with standard diesel. However, due to changes in the chemical properties when the fuels are mixed, solubility problems in terms of precipitates may be formed. These insolubilities can lead to deposits in the fuel system, e.g., blocked fuel filters and internal injector deposits, and thus driveability problems. This study is a part of a project where the goal is to study the processes that cause the formation of deposits inside the injectors in heavy-duty vehicles. The deposits inside the injectors are known as internal diesel injector deposits (IDID). To study the formation of IDID, a number of injectors from heavy duty vehicles were collected from two different European markets: one market that uses biodiesel fuel and another that uses HVO as a drop-in fuel. A technique not previously used to identify IDID, namely pyrolysis GC-MS, proved successful in this regard, and FTIR and SEM-EDX methods were also used to characterise the deposits. The results showed that the composition of the IDID´ s from different markets differed. Metal soaps, inorganic salts and nitrogen compounds were found in the deposits taken from the injectors in the biodiesel drop-in market. The source of these components is believed to be degradation and contamination of the biodiesel. In addition, fuel additives such as corrosion inhibitors and detergents were found in the injectors from the market using HVO as a drop-in fuel. This could imply that the poor solvency of HVO can give problems in some additive combinations.
Stochastic Preignition (SPI) is an abnormal combustion event that occurs in a turbocharged engine and can lead to the loss in fuel economy and engine hardware damage, and in turn result in customer dissatisfaction. It is a significant limiting factor on the use and continued downsizing of turbocharged spark ignited direct injection (SIDI) gasoline engines. Understanding and mitigating all the factors that cause and influence the rate and severity of SPI occurrence are of critical importance to the engine’s continued use and fuel economy improvements for future designs. Previous studies have shown that the heavy molecular weight components of the fuel formulations are one factor that influences the rate of SPI from a turbocharged SIDI gasoline engine. All the previous studies have involved analyzing the fuel’s petroleum hydrocarbon chemistry, but not specifically the additives that are put in the fuel to protect and clean the internal components over the life of the engine. In this study, the fuel detergent types and concentrations are compared to a baseline fuel to understand the impact of the detergent itself on the rate and severity of SPI events. The results showed that the rate of SPI increases above the baseline fuel when the concentration goes above the TOP TIER level, no matter what the detergent type. The effect of fuel detergent types and concentrations on SPI severity is found to be more complex. Despite some indications of severity reduction from one of the fuel additives at different concentrations, the variation in the behavior of base fuel with respect to the SPI severity casts doubt on the extent of this effect.
In this work, the effects of ozone, hydrogen, carbon monoxide, and exhaust gas recirculation (EGR) addition to Haltermann gasoline combustion were investigated. For these additives, laminar and turbulent flame speeds were experimentally determined using spherically propagating premixed flames in a constant volume combustion vessel. Two initial mixture pressures of Po = 1 and 5 bar, two initial mixture temperatures of 358 and 373 K and a range of equivalence ratios (Ф) from 0.5 to 1 were investigated. The additives were added as single, binary and ternary mixtures to Haltermann gasoline over a wide range of concentrations. For the stoichiometric mixture, the addition of 10% H2, 5% CO and 1000 ppm O3 shows remarkable enhancement (80%) in SL0compared to neat Haltermann gasoline. In addition, for this same blend, increasing the mixture initial temperature and pressure results in a significant increase in SL0compared to the neat gasoline. Thus it can be inferred that ternary additives suppress the reduction effect of pressure on SL0 encountered at elevated pressure with neat Haltermann gasoline. With 40% (by mass) addition of synthetic EGR (20% CO2 - 80% N2) to neat Haltermann gasoline, successful propagation of a flame was not attained; however, ternary additives blend improves the kinetics of the combustible mixture and enhances the flame propagation. The presence of a ternary additive limits the reduction of SL0 to 33% compared to base fuel (43% reduction), with a 20% EGR addition. The turbulent burning velocity at two turbulence intensities of 0.4 and 1.2 m/s showed that increasing turbulence intensity enhanced the turbulent burning velocity due to increased flame front wrinkling.
Energetic composites are mixtures of solid fuel and oxidizer particles that, when combined, offer higher calorific output than monomolecular explosives. The composites traditionally deliver energy as diffusion limited reactions and, thus, their power available from reaction is much smaller than any explosive.
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