Shizuo Yagi

Effect of Early-Closing of Intake-Valve on the Engine Performance in a Spark-Ignition Engine

In this paper we present the first stage of a study on the effect of early-closing of intake-valve on the engine performance in a spark-ignition engine. A four-valve single-cylinder engine was used with several values of expansion ratio and a half early-closing intake cam. The half early closing leads to almost a half of the volumetric efficiency and the BMEP for all cases of the expansion ratio. It can realize an improvement of about 7% in thermal efficiency under WOT, and about 4% under partial load of BMEP=0.2 MPa. These beneficial results are considered to be mainly caused by the effect of the more-expansion. The ratio of expansion to compression ratios was estimated to be around. 1.4 on the basis of motoring pressure analyses. Under the early-closing condition, an increase in the residual gas fraction was suggested and verified by a heat release analysis using a two-zone combustion model.

A Newly-Developed 1.5L CVCC Engine for Some 1980 Models

The fuel consumption and exhaust gas emission characteristics of a newly developed 1.51 CVCC engine are compared with those of a conventional engine, the pressure and temperature of combustion gas in each cylinder are measured on real time in order to clarify the differences between these characteristics, and combustion analyses are made on the basis thereof. Compared with conventional engines operated at the rich air-fuel ratio (14.7), the new CVCC engine is capable of providing, not only at the same air-fuel ratio, to be sure, but also in the lean range, a stable combustion which is small in the cycle variation, whereby the fuel consumption and emissions are improved.

Application of Over-Expansion Cycle to a Larger Gasoline Engine With Late-Closing of Intake Valves

This paper presents further investigation into the effect of over-expansion cycle with late-closing of intake valves on the engine performance in gasoline engines. A larger single-cylinder test engine with the stroke volume of 650 cc was used with four kinds of expansion ratio (geometrical compression ratio) from 10 to 25 and four sets of intake valve closure (I.V.C.) timings from 0 to 110 deg C.A. ABDC. Late-closing has an effect of decreasing the pumping work due to the reduction of intake vacuum, althogh higher expansion ratio increases the friction work due to the average cylinder pressure level. Combining the higher expansion ratio with the late-closing determines the mechanical efficiency on the basis of these two contrastive effects. The indicated thermal efficiency is mostly determined by the expansion ratio and little affected by the nominal compression ratio. The value of the indicated thermal efficiency reaches to 48% at most which is almost comparable with the value of diesel engines. The improvement of both indicated and brake thermal efficiency reaches to 16% which is much higher than ever reported by the authors. A simple thermodynamic calculation could successfully explain the behavior of the indicated thermal efficiency. The brake thermal efficiency could also be improved due to the increase in both mechanical and indicated efficiencies.Copyright