The Impact of Engine Displacement on Efficiency Loss Pathways in a Highly Dilute Jet Ignition Engine 2019-01-0330
Increasingly strict efficiency regulations for automotive applications and emissions regulations for stationary power generation applications have motivated investigation of alternative combustion modes for spark ignition engines. Ultra-lean (λ > ~1.6) combustion via air dilution is one such mode that provides the benefits of reduced fuel consumption and reduced emissions of nitrogen oxides. 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) for both stationary and range extender applications. Key results related to the optimization of the engine through enleanment and downspeeding are discussed, showing the pathways to a peak brake thermal efficiency in excess of 34%, representing a greater than 20% increase over the current state-of-the-industry for comparably sized CNG engines. An efficiency loss breakdown based on Thermodynamic First Law analysis is performed, showing trends with enleanment and engine speed. Efficiency and emissions trends with enleanment are compared with results from a larger displacement stand-alone light-duty gasoline engine also utilizing jet ignition. The comparison provides insight into how optimization parameters of the jet ignition concept can be affected by fuel source. It also serves to accentuate how performance characteristics and loss pathways of jet ignition engines change with displacement.
Nathan Peters, Michael Bunce, Hugh Blaxill