Sub-200 g/kWh BSFC on a Light Duty Gasoline Engine 2016-01-0709
Increasingly stringent global fuel economy and carbon dioxide (CO2) legislation for light duty passenger cars has created an interest in unconventional operating modes. One such mode in spark ignition (SI) gasoline engines is lean combustion. While lean operation in SI engines has previously demonstrated the ability to reduce fuel consumption, the degree of enleanment capability of the system is limited by increasingly unstable combustion in the lean region, particularly for homogeneous lean approaches. MAHLE Jet Ignition® (MJI) is a pre-chamber-based combustion system that extends this lean limit beyond the capabilities of modern SI engines by increasing the ignition energy present in the system. This allows the engine to exploit the benefits of homogeneous ultra-lean (λ > ∼1.6) combustion, namely reduced fuel consumption and reduced emissions of nitrogen oxides (NOx).
Pre-chamber combustors such as that utilized in MJI have been studied extensively for decades. Pre-chamber-based jet ignition concepts have unique features such as flame quenching and ignition site targeting that enable further system optimization. In the present study, the engine performance improvement pathways of the system are explored through an examination of experimental results from single-cylinder and multi-cylinder engines incorporating the jet igniter. System operation is presented in detail. A minimum brake specific fuel consumption (BSFC) value of 200 g/kWh and a peak brake thermal efficiency (BTE) value of greater than 41% are analyzed and discussed, as are emissions data. Performance across the engine operating map and relevant system limitations are also presented. Accurate understanding of the potential performance of the jet ignition system throughout a typical engine operating envelope can lead to further system optimization, enable concept scalability, and inform system cost-benefit analyses.