Improvement in Thermal Efficiency of a Heavy Duty Diesel Engine by High Expansion Ratio Cycle


This study is to clarify the effect of the optimum compression and expansion ratio control on the thermal efficiency by variable valve timings with a single-cylinder heavy duty diesel engine equipped with external supercharging system. Test was done in various combinations of effective compression and expansion ratio with three different pistons having different geometric compression ratios from 18.0 to 26.0. The results showed that improvement in the gross indicated thermal efficiency by increasing effective expansion ratio was still significant with the highest compression ratio, while brake thermal efficiency was deteriorated by the steeply increased mechanical and pumping losses. On the other hand, it was confirmed that the excessive exhaust heat loss caused by the reduction in heat loss from the wall was able to transform into work by adjusting effective expansion ratio larger than fixed effective compression ratio.これまでに,圧縮比と膨張比を独立に考えた場合の理論式から,有効膨張比固定で幾何圧縮比を増加させ膨張比を拡大することで熱効率の改善効果を確認した.本報は更に幾何圧縮比を増加させると共に熱損失の低減と併せた場合について図示および正味熱効率の改善の可能性を検討した.


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  • Accession Number: 01665019
  • Record Type: Publication
  • Source Agency: Japan Science and Technology Agency (JST)
  • Files: TRIS, JSTAGE
  • Created Date: Jan 31 2018 3:16PM