Today, fuel reforming is done primarily to produce hydrogen and to produce input species for fuel synthesis. Previous efforts have shown that reciprocating piston engines can be operated fuel-rich for the purpose of fuel reforming. This process is referred to as in-cylinder fuel reforming. Previous efforts have also aimed at increasing the energy conversion efficiency of systems, where a piston engine serves as a primary work producer. These have led to interest in operating direct-injection, compression-ignition (DI/CI) engines at overall stoichiometric or fuel-rich equivalence ratios. Studies have shown that the DI/CI combustion process leads to high engine-out soot. For this reason, in order to avoid excessive amounts of engine-out soot emissions, conventional DI/CI engines are usually operated at overall lean equivalence ratios
. In order to overcome this equivalence ratio barrier, while keeping the soot levels low, oxygenated fuels—fuels that contain oxygen in their molecular bonds such as methanol and ethanol—have previously shown promising results in stoichiometric DI/CI combustion strategy. Although these fuels can be difficult to auto-ignite, utilizing thermal barrier coatings on in-cylinder surfaces have resulted in reliable operation at stoichiometric conditions while keeping the soot emissions orders of magnitude below the soot levels of Diesel fuel. These developments have also enabled the use of DI/CI engines as work-producing, fuel-reforming devices operating at fuel-rich regimes. For single bulk injection, however, it was seen that the net engine-out yield significantly increased in fuel-rich equivalence ratios. This work presents original data collected on a single-cylinder, low-heat rejection (LHR), direct-injection, compression-ignition (DI/CI) engine using ethanol in stoichiometric to fuel-rich equivalence ratios. The equivalence ratio sweep of single bulk injection show that ethanol soot concentrations continue to increase up to an equivalence ratio of 1.4 and exhibit a plateau beyond this point. The experiments in this study focus on investigating the soot mitigation potential of multiple injection strategies for fuel-rich Diesel-style combustion using ethanol. In this study, the effects of multiple injection strategies on engine performance and engine-out emissions are examined. DI/CI engine’s fuel reforming capabilities under overall fuel-rich operating conditions are discussed. Observed trade-offs between soot and other performance metrics are also discussed. Experimental findings show that it is possible to mitigate engine-out soot by up to a factor of four without hindering the engine performance in fuel-rich DI/CI process, while a trade-off in the syngas yield is observed. This work is the first empirical investigation of multiple injection strategies in grossly fuel-rich regime.
