Performance of Piston Engines with Ideal Cleaning of Cylinders from Residual Gases

To increase the power produced by the engine, it is necessary to increase the mass filling of its cylinders with fresh charge.For an indirect assessment of the filling quality, the volumetric efficiency coefficient ηv is used. This coefficient characterizes not so much the filling itself as its deterioration due to the presence of residual gases, hydraulic resistances, and temperature of the fresh charge. Since the coefficient ηv depends on the parameters of the air / fresh charge at the inlet to the engine cylinders, an infinite set of values of the coefficient ηv corresponds to the same mass filling. The volumetric efficiency can be increased at the cost of losing part of the fresh charge as a result of scavenging, but this increase does not lead to an increase in power. In engines with external mixture formation, the mentioned losses mean only an increase in fuel consumption, and in diesel engines, a deterioration in environmental performance. Significantly more information about the results of filling gives the volumetric composition of the working mixture. The volume fraction of fresh charge/air in the working mixture characterizes the degree to which it fills the full volume of the cylinder, and its equality to one corresponds to the maximum possible filling, at which no residual gases remain in the cylinder. The article proposes an analysis of the impact of blowdown effects on the economic and environmental performance of the engine based on the volumetric composition of the working mixture.