The Performance and Emissions of the Turbocharged Always Lean Burn Spark Ignition (TC-ALSI) Engine 2010-01-1235
This paper extends previous development of the ALSI concept, by investigating the performance delivered with a turbocharged version of this engine.
The research is based on extensive experimental research with lean burn, high compression ratio engines using hydrogen, LPG, CNG and gasoline fuels. It also builds on recent experience with highly boosted spark ignition gasoline and LPG engines and single cylinder engine research used extensively for model calibration. The final experimental foundation is the wide ranging evaluation of jet assisted ignition that generally allows a lean limit mixture shift of more than one unit of lambda with consequential benefits of improved thermal efficiency and close to zero NOx.
The paper describes the capability of the ultra lean burn spark ignition engine with the mild boost needed provided by a Honeywell turbocharger. The concept is operation in the air-fuel ratio domain of the diesel engine but with essentially homogenous charge, although some stratification may be desirable. To achieve exceptional thermal efficiency this engine has optimised compression ratio but variable valve timing that enables reduction in the effective compression ratio under full load conditions. High specific power output is achieved by boosting the engine. To meet emission standards no NOx reduction is proposed with only an oxidation catalyst needed to meet Euro 6 standards.
The 2.6L four-cylinder engine is simulated using the group's well-developed PSO (particle swarm optimiser) engine simulation model that at a particular torque-speed, can rapidly find the local optimum engine configuration. It has been shown that the model accurately predicts the lean limit performance of both normal spark ignition and jet assisted ignition with LPG and other fuels.
Variable compression ratio is limited to 15 by mechanical constraints limit or to lower values because of knock or friction losses. Variable cam phasing is essential and results for variable inlet valve duration and fixed inlet valve duration cams are compared. In addition to power, thermal efficiency, and NOx emissions, operational characteristics of the engine are reported for optimum ignition timing, lambda, cam-phasing and boost/throttle.
The engine's maximum performance is a torque of 313 Nm and power of 147 kW with a fuel consumption reduction of around 50% over conventional SI at engine out NOx that meets Euro 6 standards.