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International Journal of Automotive Technology > Volume 2(1); 2001 > Article
International Journal of Automotive Technology 2001;2(1): 1-7.
EFFECT OF OVER-EXPANSION CYCLE IN A SPARK-IGNITION ENGINE USING LATE-CLOSING OF INTAKE VALVE AND ITS THERMODYNAMIC CONSIDERATION OF THE MECHANISM
S. SHIGA1, Y. HIROOKA2, Y. MIYASHITA1, S. YAGI3, H. T. C. MACHACON4, T. KARASAWA1, H. NAKAMURA1
1Gunma University
2Mitsui Ship Building
3Honda
4Kiryu Dai-Tchi High School
ABSTRACT
This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.
Key Words: Over-expansion cycle, Late-closing of intake valve, Intake valve timing, Pumping loss, Mechanical efficiency, Cycle efficiency, Thermodynamic estimation, T-S diagram
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