In-cylinder Fuel Reformation for High EGR Dilution SI Engines

High levels of cooled EGR have been shown to improve the fuel consumption of stoichiometric, positive ignition engines by reducing thermal losses, suppressing end gas knock, decreasing pumping losses, and improving the thermodynamic properties of the working fluid. However, the use of cooled EGR has several challenges, including control complexity, charge ignitability, combustion rates, combustion stability, combustion efficiency, and achieving adequate boost. A Dedicated EGRTM (D-EGR™) hardware configuration that enables low-loss in-cylinder fuel reformation has been proposed as a potential solution to these challenges. In-cylinder fuel reformation improves combustion and nearly recovers the flame speed, combustion stability, combustion efficiency, and ignitability deterioration associated with high levels of EGR dilution.
A turbulent vessel with schlieren photography was employed to visualize the influence of reformate on dilute ignition and combustion. Practical levels of reformate improved turbulent dilute combustion durations to within 75% of the non-dilute level with a low energy ignition system and 90% when coupled with a high energy ignition system. The accelerated combustion also significantly reduced combustion variability. In conjunction with the combustion experiments, a numerical assessment of the RON benefit from reformate was conducted on a variety of fuels. The results indicated that more than a 3 RON increase is available on-demand with in-cylinder fuel reformation. Beyond the combustion vessel work and numerical studies, two multi-cylinder engines were designed and operated to demonstrate the real-world potential of the technology. Flame speed, combustion stability, combustion efficiency and knock were all documented to improve with in-cylinder fuel reformation. The net result was a significant improvement in fuel consumption compared to baseline with stoichiometric SI efficiencies approaching a modern diesel engine while retaining the ability to use a three-way catalyst for emission control.