The Impact of Engine Displacement on Efficiency Loss Pathways in a Highly Dilute Jet Ignition Engine 2019-01-0330

Internal combustion engines currently face increasing regulatory reform which has motivated investigation of alternative combustion modes, particularly for spark ignition engines. Fuel economy regulations, among others, are presently driving the need for technological advances in the automotive sector. Stationary power generation is facing emissions standards that will be increasingly difficult to achieve with combustion-based current practices, particularly in the case of nitrogen oxides (NO_x). Ultra-lean (λ > ~1.6; air-fuel ratio > 23:1) combustion via air dilution is one such combustion mode that provides the benefits of reduced fuel consumption and reduced NO_x emissions. Jet ignition is a pre-chamber-based combustion system that enables enleanment beyond what is achievable with traditional spark ignition engines. Previous studies of MAHLE’s Jet Ignition® concept have primarily focused on light-duty gasoline engines. With increasing demand for fuel flexibility, particularly in power generation, and smaller engine displacement for range extender engines in automotive hybrid applications, it is important to characterize how the performance of this technology translates to other fuels and engine displacements.

This paper highlights results from a 390cc, high efficiency single-cylinder engine operating ultra-lean. The engine serves as a research platform for jet ignition fueled by compressed natural gas (CNG). The primary intended application is stationary power generation¹ but it is possible to ultimately extend the concept to automotive range extender applications as well given the similar two-valve configuration and cylinder displacement. An efficiency loss breakdown based on Thermodynamic First Law analysis is performed, showing that many loss pathways are found to be heavily dependent on λ. Efficiency and emissions trends are compared with results from a larger displacement stand-alone light-duty gasoline engine also utilizing jet ignition. The comparison provides insight into how parameters such as fuel and displacement affect energy loss pathways. A fuel energy breakdown of the multi-cylinder gasoline engine reveals many of the same patterns with enleanment observed with the single-cylinder CNG engine. Jet ignition and its performance in relation to engine geometry and fuel are found to alter the magnitude in which the efficiency losses change with enleanment, while preserving the same general overall trends.