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The Impact of Advanced Fuels and Lubricants on Thermal Efficiency in a Highly Dilute Engine
Abstract:
In spark ignited engines, thermal efficiency is strongly influenced by the quality of the combustion process as initiated by the ignition system. Jet Ignition is a combustion concept that utilizes a small pre-chamber to produce reactive jets which distribute ignition energy throughout the main combustion chamber. This distributed ignition energy can be leveraged to induce ignition in traditionally difficult-to-ignite regimes, such as in highly dilute mixtures. Highly dilute jet ignition combustion has been proven to produce thermal efficiencies significantly higher than those of conventional spark ignition combustion.
To fully exploit the efficiency potential of active jet ignition, multiple aspects of the engine architecture and peripheral systems must be adjusted. Efficiency sensitivities to compression ratio, boost system, and intake port design have been explored extensively. Less well understood are the sensitivities of thermal efficiency and other jet ignition combustion parameters to fuel and lubricant properties. With increasing interest in investigating fuel-engine system interactions, it is imperative to understand how future lubricants and fuels could synergistically enhance this highly efficient combustion mode.
Experimental data is obtained using a 1.5L 3-cylinder jet ignition engine. The engine is tested with a range of lubricant and fuel formulations, commercial and proprietary, at multiple compression ratios. Results are analyzed for the different fuel/lubricant/hardware combinations. High load engine operation is limited by knock, peak cylinder pressure, and peak rate of cylinder pressure rise; the governing limitation changes according to the fuel/lubricant/hardware combination being utilized, with implications for both peak load and thermal efficiency. Engine results demonstrate a peak brake thermal efficiency of 43.6% with the optimal fuel and lubricant evaluated, representing a 1.5 percentage point increase over the baseline jet ignition configuration, and a 9% improvement in cycle average fuel economy.