Study On The Ideal Cycle Of Six Stroke Diesel Engine Referring In-cylinder Rankine Cycle

Among the total energy released by the engine fuel combustion, about one third of the it is wasted in form of heat dissipation. Exhaust energy, whose temperature is high, has a high recycling value, so the recycling of it is one of the highlights in the internal combustion engine research at home and abroad. The common recovery technology of automobile exhaust energy has some different degree limitation in recovery way and efficiency, for example, exhaust gas turbo technology is very mature and widely used, but the quality of energy recycled is limited; In term of exhaust gas power generation technology, the cost and the demand of material is high, and the thermoelectric conversion efficiency is low; Coupling Rankine cycle outside the cylinder technology has complicated structure, poor adaptability of working condition and the low over all efficiency.In addition, Conklin and Szybist put forward a new type of six stroke gasoline engine, which effectively recycled exhaust gas energy, and the working state parameters in the cylinder is calculated, on the premise of setting a series of water quantity. However, this kind of design has some deficiencies, such as strict in water temperature and the waste of exhaust gas energy in the process of partial exhaust stroke and so on.In this paper, the characteristics and the insufficiency of six stroke gasoline engine proposed by Conklin and Szybist is analyzed, and another kind of six stroke diesel engine based on the Rankine cycle is put forward firstly. In order to recover exhaust gas energy in cylinder, working principle of diesel engine based on Rankine cycle coupled in cylinder is designed; Ideal cycle is constructed, that is the first four ideal cycle(intake, compression, and work schedule) is the same as diesel engine ideal cycle, and the increased ideal cyclic process is exhaust isentropic compression process, exhaust isochoric volume reduction process(water remain liquid water), liquid water special instantaneous vaporization process, exhaust gas and steam mixed gas isentropic expansion. Based the ideal cycle, relevant mathematical model is constructed and thermal efficiency is calculated theoretically. The calculation content included state properties in the fourth and fifth stroke and increased indicated work; besides, influence of water injection timing and water quality on the properties and the increased indicated work is studied.Results indicate that thermal efficiency is improved by combining Diesel cycle with Rankine cycle in cylinder; the later water is injected and the more the water quality is, the less the increased indicated work is. At the same time, it is forecasted theoretically that emissions of HC, PM and NOX will reduce for the engine possibly.