Current combustion systems predominantly are ?single-fuel? devices. For example, the ubiquitous spark ignition engine routinely uses gasoline as a fuel, while the typical compression ignition engine uses diesel as a fuel. There are well-founded reasons for this existing paradigm. In simple terms, the high volatility of gasoline makes it amendable for pre-cylinder (or early direct-cylinder injection) vaporization and subsequent premixing. Likewise, the high ignitability of diesel fuel makes it appropriate for compression ignition. The past century of engine development, however, has witnessed tremendous growth and advancement of both spark- and compression-ignition engines. A reasonable question becomes, what?s the best fuel for the advanced combustion engine? Some preliminary efforts have suggested that the best fuel may in fact be a combination of two fuels. Specifically, the Reactivity Controlled Compression Ignition mode of combustion ? which is a type of low temperature combustion ? uses both a highly volatile fuel (such as gasoline) along with a highly ignitable fuel (such as diesel) in the same apparatus. This shift in the paradigm requires exploration of other qualifying fuels, particularly alternative fuels, in an effort to discern if this radically different approach may yield the high payoff it potentially promises. Several research questions exist regarding such science, including how the fuels? interactions may affect chemistry of the reaction, how physical fluidic processes (such as penetration, breakup, atomization, and vaporization) are affected by the presence of a potentially reactive mixture, and how soot formation processes are affected by the interaction with a reactive mixture. This research aims to explore the viability of hydrous ethanol and biodiesel as fuels in dual-fuel reactivity controlled compression ignition (RCCI) low temperature combustion mode in a medium-duty diesel engine and to compare their response ? in terms of engine power, efficiency, and in-cylinder processes (such as fluid processes, chemistry, and emissions formation) ? with RCCI using conventional gasoline and diesel fuels. The overarching benefit of RCCI seems to be that it can simultaneously reduce NOx and soot from diesel engines while also maintaining high efficiency and specific power. The research makes use of experimental engine research facilities with controlled studies of the fuel and air mass and rate of reaction.
This research intends to improve the end use efficiency of work conversion devices (such as combustion engines) while maintaining environment quality (i.e., low emissions) and assessing the viability of alternative fuels in combustion systems. Implementation of RCCI results in high chemical-to-work conversion efficiencies while maintaining low formation rates of nitrogen oxides and soot, both which contribute to poor atmospheric quality and local SMOG. The attainment of high efficiency combustion systems, particularly with the use of bio-based alternative fuels, allows society to move toward carbon-neutrality. Additionally, the research will further efforts to recruit and educate underrepresented students through hands-on experimental research. Funds will be leveraged to support graduate and undergraduate research to improve the number of students formally educated in STEM disciplines.
Current combustion systems predominantly are "single-fuel" devices. For example, the ubiquitous spark ignition engine routinely uses gasoline as a fuel, while the typical compression ignition engine uses diesel as a fuel. There are well-founded reasons for this existing paradigm. In simple terms, the high volatility of gasoline makes it amendable for pre-cylinder (or early direct-cylinder injection) vaporization and subsequent premixing. Likewise, the high ignitability of diesel fuel makes it appropriate for compression ignition. The past century of engine development, however, has witnessed tremendous growth and advancement of both spark- and compression-ignition engines. A reasonable question becomes, what’s the best fuel for the advanced combustion engine? Some preliminary efforts have suggested that the best fuel may in fact be a combination of two fuels. Specifically, the Reactivity Controlled Compression Ignition mode of combustion – which is a type of low temperature combustion – uses both a highly volatile fuel (such as gasoline) along with a highly ignitable fuel (such as diesel) in the same apparatus. This shift in the paradigm requires exploration of how common engine control parameters (e.g., fuel injection timings, intake manifold pressures, and exhaust gas recirculation levels) influence engine performance and emissions under dual-fuel operation. Several research questions exist regarding such science, including how the fuels’ interactions may affect chemistry of the reaction, how physical fluidic processes (such as penetration, breakup, atomization, and vaporization) are affected by the presence of a potentially reactive mixture, and how soot formation processes are affected by the interaction with a reactive mixture. This exploratory research project uncovered several important components to help direct the next stages of research into dual-fuel engine operation. Specifically, the key outcomes, which constitute the intellectual merits, of the research include: The important parameters influencing efficiency and emissions in dual-fuel operation were identified through regression of design-of-experiments (DOE) - oriented test results: gasoline fraction, injection timing, rail pressure, intake pressure, and EGR level. The significance of the above parameters were quantified: whether they have significant or insignificant, positive or negative influence on efficiency and emissions. This is indicated by regression models that were developed as part of the project. Researchers can use these models to investigate the influence of various parameters on engine efficiency and emissions in their similar dual-fuel research. For example, to improve efficiency in dual-fuel operation at medium load, intake pressure needs to be decreased, injection timing advanced, EGR level and gasoline fraction increased. The parameter settings for better efficiency and emissions in diesel operation and dual-fuel operation at low load and medium load are obtained through regression and verified through tests. Researchers can use the parameter settings determined from this research to get better engine efficiency and emissions in their similar dual-fuel research. The engine can be viewed as a black box, producing corresponding output of engine efficiency and emissions with suitable input of parameter settings. A guideline is provided to direct DOE-oriented development of dual-fuel engine research, which can identify the relationship among parameters and efficiency and emissions: define target, select parameters and levels, select design arrays, do tests, statistical analysis of results, find best models, optimization to find best parameter settings, confirmation tests. A guideline is provided to apply cyclic variability (CV) analysis to the development of dual-fuel engine research in order to improve CV of combustion and performance: identify parameters to calculate for each cycle, acquire high-speed data from consecutive cycles in engine test, analyze sources of CV, analyze CV in terms of magnitude using "cyclic spread" of high-speed profiles and COV of parameters, and analyze CV in terms of determinism using probability density function, autocorrelation coefficient, return map, and symbol sequence statistics method. A few gaps shown by the current state-of-the-art dual-fuel research are filled by this study. Dual-fuel operation is done with gasoline fumigation on a four-cylinder medium-duty diesel engine. Gasoline fumigation not only simplifies control strategy but also reduces hardware cost. Cylinder balancing is used to improve cylinder variation. DOE and relevant statistical techniques are used to aid the development. Cyclic variability was studied in dual-fuel operation and its influence on engine performance and efficiency. The broader impact of the research relates to its overarching goal of improving end use efficiency while maintaining environment quality (i.e., low emissions). Additionally, the research furthered the PIs efforts to recruit and educate underrepresented students through hands-on experimental research. Further, the PI leveraged the awarded funds to continue to support undergraduate research through an NSF REU site located at Texas A&M. Finally, the PI used the awarded funds to support a graduate student to conduct the research and disseminate the research through common and appropriate channels including scholarly journals, conference papers, and technical workshops.
