Abstract
This paper describes the turbocharged ALSI engine concept. The research is based on extensive experimental research with lean burn, high compression ratio engines. It also builds on recent experience with highly boosted spark ignition gasoline and LPG single cylinder engine research used extensively for model calibration. The final foundation is a wide ranging evaluation of jet assisted ignition that usually allows a lean mixture shift of more than one lambda unit and thus improved thermal efficiency and almost zero NOx. The capability of the ultra lean burn spark ignition engine is described, with the mild boost needed provided by a turbocharger. The concept is operation in the domain of the diesel engine but with essentially homogenous charge. To achieve exceptional thermal efficiency this engine has optimised compression ratio fixed at 15 limited by mechanical constraints but variable cam phasing enabling reduction in the effective compression ratio under full load conditions. High specific power output is achieved by boosting the engine. The 4 L six-cylinder engine was initially simulated using the research group’s PSO (particle swarm optimiser) engine simulation model that at a particular torque-speed, can rapidly find the local optimum engine configuration. The simulation results are repeated using the commercial simulator GT Power. In addition to power, and thermal efficiency, operational characteristics of the engine are reported: optimum ignition timing, lambda, cam-phasing and cam overlap, boosted/throttled operation.
The engine’s maximum performance is predicted as a torque of 405 Nm and power of 210 kW with a fuel consumption reduction, based on NEDC steady state mapping points, of around 33% for a base SI car of 1704 kg mass and with a consumption of 9.8 L/100km.
Keywords: High efficiency, ultra lean burn, jet ignition, modelling, gasoline.