Optimizing Thermal Efficiency of a Multi-Cylinder Heavy Duty Engine with E85 Gasoline Compression Ignition

Gasoline compression ignition (GCI) using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low-temperature combustion with low engine-out NO_x and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation (EGR)) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high temperature combustion with reduced amounts of EGR appears more practical. Previous studies with 93 AKI gasoline demonstrated that the port and direct injection strategy exhibited the best performance, but the premature combustion event prevented further increase in the premixed gasoline fraction and efficiency. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high temperature GCI combustion using E85 gasoline. The impact on engine performance and emissions was evaluated at an engine speed of 1038 rpm and brake mean effective pressure of 14 bar with port and direct injection strategy. Compared to previous gasoline results, the start of combustion was significantly retarded and the premixed combustion was more pronounced with E85. The combustion phasing, premixed fuel amount, and pumping losses were optimized to improve efficiency by adjusting main/pilot injection timing, port/pilot injection mass fraction, and turbo charger settings. Overall, the brake thermal efficiency with E85 was 1.2% and 0.5% higher compared to the diesel baseline and E85/diesel dual-fuel combustion, respectively. E85 showed near zero soot emissions and a more than 70% reduction in NO_x emissions compared to diesel.