Design and development of a jet ignition engine for stable ultra-lean operation

摘要

Driven by legislation, social consciousness, and market demand, the automotive sector has been seeking technologies to significantly increase the efficiency of the internal combustion engine in order to conserve fuel resources. Lean combustion in spark ignition (SI) gasoline engines is a well understood method for increasing brake thermal efficiency (BTE). Near-lean operation (1<λ<1.3), while increasing thermal efficiency, also produces increases in engine-out emissions of nitrogen oxides (NO_x). Combustion stability degrades with enleanment, which results in a lean limit for SI engines. Consequently, homogeneous SI combustion is generally limited to near-lean operation. Ultra-lean operation (λ≥2) has demonstrated the ability to simultaneously increase thermal efficiency and significantly reduce NO_x emissions. Jet Ignition, a pre-chamber-based combustion system, is one such enabling technology. Several previous studies from the authors [1,2] have proven that a Jet Ignition concept can achieve stable ultra-lean operation in a light duty engine, producing a minimum brake specific fuel consumption (BSFC) value below 200 g/kWh with simultaneous engine-out NO_x emissions less than 100 ppm. Ultra-lean combustion generally and Jet Ignition specifically place unique demands on the engine and supporting systems. Lower exhaust enthalpy resulting from colder exhaust temperatures associated with ultra-lean operation necessitates changes to the boost system. This study seeks to quantify the changes needed to a base engine and boost system to optimize the resulting Jet Ignition engine. A baseline multi-cylinder Jet Ignition engine is tested and performance and emissions data is presented. This data is input to 1D simulations used to evaluate the efficacy of a variety of commercially available boost systems for this ultra-lean application. The boost system evaluation is performed on a dedicated 3-cylinder Jet Ignition engine that will be optimized specifically for Jet Ignition operation. This engine will be assembled and tested, and will be used to confirm the simulation results presented here in a subsequent study.