Piston Pre-Heating Using a Pressurized-Heated Oil Buffer: A Practical Method to Reduce ICE Emissions and Fuel Consumption

Engine cold start is characterized by sub-optimal combustion efficiency due to the low temperature of the combustion chamber; this heavily increases engine raw emissions at start. One driving phenomenon is a limited fuel evaporation rate. Consequently, a liquid fuel film remains on the piston top at ignition. Liquid fuel deposited on the piston top is a well-known cause of “pool-fire”, leading to high levels of particle emissions; a problem particularly noticeable with bio-based renewable fuels. Engine piston pre-heating can be deployed to prevent or limit the formation of such fuel film and associated pollutants. In this work a practical technique is proposed to effectively pre-heat the pistons immediately before engine cold start. The device consists of a pressurized-heated oil buffer which pre-heats the pistons via the existing piston cooling nozzles. The device provides further benefits in emissions and fuel consumption in two ways: 1) the warm oil pre-lubricates the engine working surfaces reducing friction and 2) reducing the engine thermal inertial by reducing the active oil mass. The first part of this work is a detailed summary of numerical and experimental analysis evidencing the benefits of piston and engine oil pre-heating. The study suggests a near complete evaporation of the fuel film on the piston top at ignition timing, primary source of cold start particle emissions and a reduction in HC due to the favorable combustion chamber preconditioning. Emissions are further lowered by the reduced engine friction due to oil and bearing pre-heating. Moreover, lower engine friction and higher combustion efficiency return a decrease in vehicle fuel consumption. The second part of this work describes the pressurized oil buffer working principles, its pros and cons. The third part elaborates on the implementation strategy and synergies of the oil buffer with different powertrains and application scenarios.