Relation between Valve Angle-Area and Low Speed Performance of a Uniflow-Scavenged Engine

Abstract

In order to find the optimum angle-area of the exhaust valve of a two-stroke engine as a function of engine speed, performance tests were carried out with a uniflow-scavenged diesel engine at various speeds under large valve-clearance. The test result showed that the minimum point of indicated specific fuel consumption curve shifted towards lower speed with decreasing valve anglearea, i.e. increasing valve clearance. By analyzing the test results it was theoretically ascertained that the improvement in performance at lower engine speed is mainly due to a decrease in blowdown loss and an increase in charging efficiency. An attempt was then made to control the valve angle-area automatically according to engine speed, by means of a hydraulic tappet with a leak hole, presented in the previous paper. The diameter of the leak hole was chosen so as to give appropriate angle-area for better performance at lower speed on the basis of the above discussion. A performance test with the device showed that fuel consumption improved over the lower speed range, especially under heavy load. The fuel consumption vs. engine speed curve approximately forms an envelope of the ones obtained in preceding tests. However, this tappet has a drawback of high valve seating velocity. This problem must be solved for practical use.