6. Opposed-Piston Gasoline Compression Ignition Engine

Gasoline compression ignition (GCI) is an approach to achieving diesel-like efficiencies but with potentially lower cost and fewer emissions. Traditional challenges with GCI arise at low-load conditions due to low charge temperatures causing combustion instability and at high-load conditions due to peak cylinder pressure and noise limitations. The fundamental architecture of the two-stroke Opposed-Piston Engine (OP Engine) enables GCI by decoupling piston motion from cylinder scavenging, allowing for flexible and independent control of cylinder residual fraction and temperature leading to improved low-load combustion. In addition, the high peak cylinder pressure and noise challenges at high-load operation are mitigated by the lower BMEP operation and faster heat release for the same pressure rise rate of the OP engine. These advantages further solidify the performance benefits of the OP engine and demonstrate the near-term technical feasibility of advanced combustion technologies, enabled by the opposed-piston architecture. This chapter describes the architectural advantages of the OP engine for GCI and presents testing results of a 2.7L OP GCI multi-cylinder engine. A part of the recipe for successful GCI operation calls for high compression ratio, leading to higher combustion stability at low-loads, higher efficiencies, and lower cycle HC + NO_x emissions. In addition, results on catalyst light-off mode with GCI are also presented. The OP engine’s architectural advantages enable faster and earlier catalyst light-off while producing low emissions, which further improves cycle emissions and fuel consumption over conventional engines.