Browse Topic: Reformulated gasoline
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.
For controlling oxides of nitrogen (NOx) and particular matter (PM) emissions from diesel engines, various fuel and combustion mode modification strategies are investigated in the past. Low temperature combustion (LTC) is an alternative combustion strategy that reduces NOx and PM emissions through premixed lean combustion. Dual fuel reactivity-controlled compression ignition (RCCI) is a promising LTC strategy with better control over the start and end of combustion because of reactivity and equivalence ratio stratification. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are significantly higher in RCCI, especially at part-load conditions. The present work intends to address this shortcoming by utilizing oxygenated alternative fuels. Considering the limited availability and higher cost, replacing conventional fuels completely with alternative fuels is not feasible. Based on this premise, oxygenated alternative fuel blends, viz. methanol and Karanja biodiesel with 20 vol. % in gasoline and diesel, respectively, is used as a port and direct-injected fuels in RCCI. A light-duty diesel engine used for agricultural water pumping applications is modified to run in RCCI through suitable intake and fuel injection systems modifications. The engine combustion, performance, and exhaust emissions with oxygenated fuel blends are compared with gasoline and diesel as a port and direct-injected reference fuels. The results obtained show that the HC emissions are reduced by up to 44% with oxygenated fuel blends. Further, the indicated thermal efficiency is increased by ~20%, and the indicated specific fuel consumption is reduced by ~10% with oxygenated alternative fuel blends. Overall, fuel-bound oxygen and a much wider reactivity variation with oxygenated alternative fuel blends result in improved combustion efficiency, lower HC emissions, and higher thermal efficiency in RCCI. Thus, oxygenated alternative fuel blends could be a promising option to improve combustion efficiency in RCCI.
The use of alternative fuels, especially oxygenated fuels in automobile engines, has been increasing owing to the stringent global fuel economy and emission regulations. As a result, it is concerned that the emissions of alcohols and aldehydes have increased significantly. Aldehydes, formaldehyde (HCHO) in particular, are non-criteria pollutants that are acutely toxic and/or carcinogenic. Several reports have associated HCHO with potential lung and airway cancers. Therefore, emission regulations for these compounds have already been implemented in several areas worldwide. The conventional measurement (impinger, etc.) methods for HCHO possess advantages and disadvantages. HCHO can be measured with high sensitivity if measured in a batch. However, in real-time measurements, low concentration measurements are challenging. To overcome this challenge, a real-time HCHO analyzer for low concentration measurement of 0.1 ppm resolution in real time of 10Hz was developed in this study based on laser spectroscopic principles. The results in this study highlight the fundamental performance of the method and application to real automobile exhaust gas measurements.
Alcohol-based fuels are a viable alternative to fossil fuels for powering vehicles. As a drop-in fuel, an oxygenated fuel blend containing the C8 alcohol 2-ethylhexanol (isomer of octanol), hydrotreated vegetable oil (HVO) and rapeseed methyl ester (RME) can reduce soot and NOx emissions whilst maintaining engine performance. However, fuel injection strategy significantly affects combustion and hence has been investigated with a view to reducing emissions whilst maintaining engine efficiency. In a single cylinder light-duty compression ignition research engine, the effect of different injection strategies (main, main/post, double pre/main, double pre/main/post injection) and EGR levels (0%, 19%) on specifically NOx, soot emissions and particle size distribution was investigated for three different fuels: fossil diesel fuel, HVO and the oxygenated blend. The blend was designed to have diesel-like combustion properties (cetane number of 52) and had an oxygen content of 5.4% by mass. The crank angle used when measuring MFB50, fuel consumption and IMEP was kept constant. The engine efficiencies were similar for all tested fuels and injection strategies. Heat release analysis revealed a strong influence of the cetane number on main and main/post injection strategy. However, when using double pre-injection, the start of combustion was similar for all fuels. Combustion characteristics, particle mass and number were more affected when using double pre-injection rather than post-injection. With 19% EGR and double pre-injection, soot mass increased as agglomerated particle mode increased in the PSD. Further, the in-cylinder temperature and pressure were lower compared to combustion without EGR, leading to a reduction of NOx emissions by a factor of 2.5 while soot emissions increased by a factor of 10. There were just minor differences in NOx emissions with variations in injection strategy. The PSD moved towards smaller particle diameters without EGR. In conclusion, the soot reduction potential of all fuels tested was coupled to the use of double pre-injection and EGR rather than post-injection.
Mixture formation in GDI engine is considered crucial in determining combustion and emissions characteristics, which mainly depend on fuel spray quality. However, spray characteristics change with variations in control parameters such as fuel injection parameters, fuel injection strategy, engine operating conditions, and fuel properties. Growing research interest in the use of methanol as an additive with gasoline has motivated the need for deeper investigations of spray characteristics of these fuels. Although, it can be noted that sufficient literature is available in the area of spray characterization under several independent influencing factors, however, comparative analysis of gasohol spray behavior under different ambient conditions is hardly studied. This study is aimed at investigating the spray morphology, and evaporation and mixing characteristics of M15 (15% v/v methanol in iso-octane) and M85 (85% v/v methanol in iso-octane) in comparison to iso-octane at early injection and late injection conditions. CFD simulation studies were performed using multi-hole GDI injector in a constant volume spray chamber (CVSC) using Converge software. Numerical model used for the analysis was validated using experimental spray penetration measurements, available at the ECN. The results highlighted that effect of methanol properties on spray penetration and SMD of fuel droplets diminished under high temperature-high pressure conditions. Although, substantial difference in droplets evaporation was found among the test fuels due to inferior volatility of methanol, which definitely demands optimization of fuel injection parameters for adapting methanol blends in the engine. However, despite lower droplet evaporation, equivalence ratio distribution for methanol blends was more shifted towards stoichiometric conditions due to inherent fuel oxygen content.
In this study, a fully optically accessible single-cylinder research engine is the basis for the visualization and generation of extensive knowledge about the in-cylinder processes of mixture formation, ignition and combustion of oxygenated synthetic fuels. Previous measurements in an all-metal engine showed promising results by using a mixture of dimethyl carbonate and methyl formate as a fuel substitute in a DISI-engine. Lower THC and NOx emissions were observed along with a low PN-value, implying low-soot combustion. The flame luminosity transmitted via an optical piston was split in the optical path to simultaneously record the natural flame luminosity with an RGB high-speed camera. The second channel consisted of OH*-chemiluminescence recording, isolated by a bandpass filter via an intensified monochrome high-speed camera. To investigate the combustion process spectrally, spatially and temporally resolved in more detail, selected operating points were recorded again via a high-speed imaging spectrograph. Regular gasoline fuel acts as a reference and is compared to the oxygenated mixture. Since all oxygenated fuels show a heating value lower than gasoline, the injected mass increases for constant engine load. For 65 vol-% DMC 35 vol-% MeFo, the gasoline equivalent, a product of the lower heating value and the density, results in a factor of two. Accordingly, elevated cooling effects of the mixture are expected. Because of these unfavorable conditions for mixture formation, spots of diffusion flames could be detected when using oxygenated fuels. A lambda sweep showed that the mixture did not produce significant soot even in slightly lower than stoichiometric conditions. In addition, a very late SOI of around 90 CAD bFTDC showed reduced burning duration and lower diffusion flame intensity.
To characterize the effects of renewable fuels on particulate emissions from GDI engines, engine experiments were conducted using EN228-compliant gasoline fuel blends containing no oxygenates, 10% ethanol (EtOH), or 22% ethyl tert-butyl ether (ETBE). The experiments were conducted in a single cylinder GDI engine using a 6-hole fuel injector operated at 200 bar injection pressure. Both PN in raw exhaust and solid PN (SPN) were measured at two load points and various start of injection (SOI) timings. Raw PN and SPN results were classified into various size ranges, corresponding to current and future legislations. At early SOI timings, where particulate formation is dominated by diffusion flames on the piston due to liquid film, the oxygenated blends yielded dramatically higher PN and SPN emissions than reference gasoline because of fuel effects. For particulates >23 nm and with optimized SOI timing, the use of oxygenated blends significantly increases SPN and conversely decreases raw PN emissions at low load (4.5 bar IMEP). At high load (9 bar IMEP), overall SPN emissions were significantly higher and there were no clear differences between the blends. Additionally, SPN measurements showed that soot formation and emissions of volatile organic compounds (VOC) depended strongly on blend composition. Finally, adding oxygenates (up to 22%) to gasoline did not reduce emissions of SPN in the size ranges addressed by current regulations.
Diesel-fueled compression ignition engines display a distinct trade-off in particulate matter (PM) and nitrogen oxide (NOX) emissions due to the nature of diffusive combustion. The modification of fuel properties has drawn much attention since these methods offer additional potential to reduce emissions. Oxygenated fuels are reported to greatly diminish particle emissions while water emulsification of regular diesel causes a significant decrease in NOX. However, recent studies indicate that these fuel-based approaches may lead to an increase in nanoparticle emissions, which are known to be more dangerous to human health than large particles. This has raised the question about whether current engine technology is prone to nanoparticle formation. In this work, the authors present a detailed study on combustion and emission performance of the oxygenate fuel Oxymethylene Ether (OME n , the mixture contains neat OME with chain length n = 2 − 6). In a novel approach, a single-cylinder heavy-duty diesel engine was fueled with both neat and water-emulsified OME to combine the two fuel-based methods in order to simultaneously reduce both NOX and particle emissions to a great extent. Particular emphasis was put on the particle size distribution (PSD) of emitted PM to elaborate a potentially severe drawback of these fuel-based approaches. In the process, hydrogenated vegetable oil (HVO) was used as the diesel reference fuel. The findings are summarized as such: PSD measurements of OME2-6 reveal similar particle diameters in mid-load operation and a shift to smaller particles at unfavorable engine operations compared to HVO. Water-emulsified OME2-6 reduces NOX by roughly 2-3% with a one percent increase in water concentration while maintaining a nearly constant combustion efficiency. Adverse effects on nanoparticle formation by water emulsification were not observed.
With the aim of identifying technical solutions to lower the particulate matter emissions, the engine research community made a consistent effort to investigate the root causes leading to soot formation. Nowadays, the computational power increase allows the use of advanced soot emissions models in 3D-CFD turbulent reacting flows simulations. However, the adaptation of soot models originally developed for Diesel applications to gasoline direct injection engines is still an ongoing process. A limited number of studies in literature attempted to model soot produced by gasoline direct injection engines, obtaining a qualitative agreement with the experiments. To the authors’ best knowledge, none of the previous studies provided a methodology to quantitatively match particulate matter, particulate number and particle size distribution function measured at the exhaust without a case-by-case soot model tuning. In the present study, a Sectional Method-based methodology to quantitatively predict gasoline direct injection soot formation is presented and validated against engine-out emissions measured on a single-cylinder optically accessible gasoline direct injection research engine. While adapting the model to the gasoline direct injection soot framework, attention is devoted to modelling the dependence of the processes involved in soot formation on soot precursors chemistry. A well-validated chemical kinetics mechanism is chosen to accurately predict soot precursors formation pathways retaining an accurate description of the main oxidation pathways for oxygenated fuel surrogates. To account for the prominent premixed combustion mode characterizing modern GDI units, a constant pressure reactor library is generated containing the rates for the chemistry-based processes involved in soot formation and evolution at engine-like conditions. The proposed methodology is successfully applied to a 3D computational fluid dynamics model of the engine to predict soot engine-out emissions at the exhaust.
The Federal reformulated gasoline (RFG) program originated with the 1990 Clean Air Act Amendments to address high ozone and air toxics levels in major urban areas. These areas include portions of 17 states and represent approximately 30% of the total U.S. gasoline volume. Initially, formulation changes were limited to addition of oxygen and reductions in benzene and fuel Reid vapor pressure (RVP) levels. These reformulations were intended to meet minimum emissions reduction targets for volatile organic compounds (VOCs), air toxics, and oxides of nitrogen (NOx) when compared to a 1990 baseline gasoline in a “1990 technology” vehicle fleet. The United States Environmental Protection Agency (U.S. EPA) developed two computational models, the Simple Model in 1995 and the Complex Model in 1998, for use in demonstrating compliance with the regulations. This article reviews the derivation and evolution of the RFG program. Initially, RFG’s emissions reduction benefits compared to conventional gasoline (CG) resulted primarily from differences in fuel sulfur levels, benzene content, and RVP. However, due to other regulatory changes over the past two decades, the compositions of CG and RFG have nearly converged. Inserting annual average gasoline properties into the Complex Model shows that RFG’s predicted NOx and toxics reduction benefits have largely disappeared, while a VOC reduction benefit persists. This benefit results from CG’s higher summertime vapor pressure, due to the 1 psi RVP increase that is allowed for CG containing 10 vol.% ethanol. Due to fleet turnover and introduction of low-emitting, advanced technology vehicles, fleet-wide vehicle emissions have decreased dramatically over the past 20 years. Considering this, along with the general erosion of RFG’s emissions reduction benefits, it is unlikely that RFG provides any demonstrable air quality benefit compared to CG today. RFG’s residual VOC benefit likely could be maintained by application of simpler RVP controls, rather than by continuation of the outdated RFG program.
Piston wetting can be isolated from the other sources of HC emissions from DISI engines by operating the engine predominantly on a gaseous fuel and using an injector probe to impact a small amount of liquid fuel on the piston top. This results in a marked increase in HC emissions. All of our prior tests with the injector probe used California Phase 2 reformulated gasoline as the liquid fuel. In the present study, a variety of pure liquid hydrocarbon fuels are used to examine the influence of fuel volatility and structure. Additionally, the exhaust hydrocarbons are speciated to differentiate between the emissions resulting from the gaseous fuel and those resulting from the liquid fuel. It is shown that the HC emissions correspond to the Leidenfrost effect: fuels with very low boiling points yield high HCs and those with a boiling point near or above the piston temperature produce much lower HCs. As expected, there is a significant effect of fuel structure for fuels that have the same boiling point. For fuels with the same boiling point, the primary effect of structure appears to be its effect on unburned fuel emissions.
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