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Schematic constructions of a proposed six-stroke diesel engine and a conventional four-stroke diesel engine . This six-stroke diesel engine was made from a conventional four-stroke diesel engine with some modification. A sub-shaft was added to the engine, in order to drive a camshaft and injection pumps. The rota­tion speed of the sub-shaft was reduced to 1/3 of the rotation of an output shaft. To obtain similar valve timings between a four-stroke and a six-stroke diesel engine, the cam profile of the six-stroke diesel engine was modified. In order to separate the fuels, to control each of the injec­tion timings and to control each injection flow rate in the first and the second combustion processes, the six-stroke diesel engine was equipped with two injection pumps and two injection nozzles. The injection pumps were of the same type as is used in the four-stroke diesel engine.

Details of nozzle position of the four-stroke diesel engine are shown in The nozzle is located near the center of a piston cavity, and has four injection holes. For the six-stroke diesel engine, one extra nozzle was added on This extra nozzle was of the same design as that of the four-stroke engine.

Diesel fuel for the first combustion process was injected through this extra nozzle, and methanol for the second combustion process was injected through the center noz­zle. Here, we denoted the injection timing of the four­ stroke diesel engine. The injection timings of the first and second combustion strokes for the six-stroke diesel engine, respectively. Crank angle was measured from the intake. In the six-stroke engine, crank angle of the first combustion is 180 degrees. The second combustion TDC is 540 degrees.

Specifications of the test engines. The conventional four-stroke diesel engine that was cho­sen as the basis for these experiments was a single cylin­der, air cooled engine with 82 mm bore and 78 mm stroke. The six-stroke engine has the same engine speci­fications except for the valve timings. However, the volu­metric efficiency of the six-stroke engine showed no significant difference from that of the four-stroke engine.

Characteristics of the six-stroke diesel engine were com­pared with the conventional four-stroke diesel engine. In this paper, the engine speed (Ne) was fixed at 2,000 rpm. Cylinder and line pressure indicators were equipped on the cylinder head. NO concentration was measured by a chemiluminescence’s NO meter, and soot emission was measured by a Bosch smoke meter


A four-stroke engine has one intake stroke for every two engine rotations. For the six-stroke engine, however, the intake stroke took place once for every three engine rotations. In order to keep the combustion heat per unit time constant, the combustion heat supplied to one six-stroke cycle should be 3/2 times larger than that of the four-stroke engine.

There are many ways to compare performance between the four-stroke and six-stroke engines. For this paper, the authors have chosen to compare thermal efficiency or S.F.C. at same output power. If the thermal efficiency was the same in both engines, the same output power would be produced by the fuels of equivalent heats of combus­tion. Therefore, in order to make valid comparison, fuels supplied per unit time were controlled at the same value for both engines and engine speeds were kept constant. In this section, fuel supplied for the engines was only a diesel fuel. Performance of the six-stroke engine was compared with that of the four-stroke engine under vari­ous injection timings.

Exhaust NO, soot emissions, and indicated torque of the four-stroke and the six-stroke engines are Detailed conditions for comparison of the four-stroke and six-stroke engines are listed The heat allocation ratio of the six-stroke engine was set at αH = 0.5. Injection flow rate of fuel was Qt4 = 0.50 kJ/cycle for the four-stroke engine and Qt6 = 0.68 kJ/cycle for the six stroke engine. For six stroke engine, it meant that ­the amount of 0.34kj was supplied at each combustion process. At the viewpoint of combustion heat, 075 kj/cycle of heat should be supplied for the six stroke engine to make the equivalence heat condition. However diesel fuel of 0.68 kj/cycle was supplied here because of difficulties associated with methanol .