High Compression Ratio Active Pre-chamber Single-Cylinder Gasoline Engine with 50% Gross Indicated Thermal Efficiency.

ABSTRACT

Active pre-chamber turbulent jet ignition with a high compression ratio has been demonstrated to be an effective method for significantly enhancing engine thermal efficiency. A dual modification of the combustion chamber and the pre-chamber was performed on an AVL 5400 single-cylinder Miller engine to achieve stable ultra-lean burn at a high compression ratio, and a breakthrough of 51.10% gross indicated thermal efficiency was achieved at the compression ratio of 16.4 and λ = 2.236. Spark ignition and pre-chamber turbulent jet ignition exhibit significant performance diversities under lean burn conditions. Pre-chamber turbulent jet ignition is able to significantly expand the lean burn limit of spark ignition to λ = 2.7 (CoVIMEP < 5%) at only the expense of an increased HC emission, while apparently reducing fuel consumption and nitrogen oxide emissions. With an increase in the compression ratio from 13.6 to16.4, spark ignition and pre-chamber turbulent jet ignition exhibit contradictory performance laws. The engine performance of a spark ignition engine decreases significantly as the compression ratio increases, whereas a pre-chamber jet ignition engine can still operate reliably at a high compression ratio with ultra-lean combustion. Within the scope of the test, the performance of the pre-chamber jet ignition engine is enhanced by a greater compression ratio. This improvement is primarily attributable to the reduction of heat transfer loss and exhaust energy loss under ultra-lean combustion, as determined by an analysis of the structure of power losses.