Thermal efficiency improvement of super-lean burn spark ignition engine by stratified water insulation on piston top surface

Tsuyoshi Nagasawa, Yuichi Okura, Ryota Yamada, Susumu Sato, Hidenori Kosaka, Takeshi Yokomori, Norimasa Iida

研究成果: Article査読

6 被引用数 (Scopus)

抄録

In order to improve thermal efficiency of spark ignition engine under super-lean burn conditions (excess air ratio (Formula presented.)), thermal stratification technique by in-cylinder water injection toward piston surface (stratified water insulated combustion architecture), in which low temperature water vapor layer is formed on the surface, is proposed. From the water spray visualization using the optically accessible engine, injected water is distributed near the piston top surface at ignition timing and thermal stratification can be achieved in the case that water injection timing (SOIw) is set at earlier stage of a compression stroke. In addition, heat flux on the piston surface measured at the same time is reduced by water injection. The 0.5-L single-cylinder engine test at λ = 2.0 at a constant ignition timing also shows that water injection at earlier stage of a compression stroke makes it possible to mitigate knock without significant increase in combustion instability. On the other hand, part of water is distributed near the spark plug at ignition timing with the water injection at SOIw = −60 °ATDC, resulting in unstable combustion. In addition, the engine test at λ = 2.0 and water/fuel ratio(W/F) = 18% shows that knock mitigation by water injection enables spark advance and following combustion enhancement. As a result, combustion period becomes short and cooling loss decreases, followed by the 1.0-pt improvement of gross indicated thermal efficiency. Moreover, the engine can be operated at minimum spark advance for best torque by increasing W/F up to 35%. Finally, stratified water insulated combustion architecture concept is applied at λ = 1.9 with a higher compression ratio of 17, showing that water injection at SOIw = −120 °ATDC and W/F = 50% enables minimum spark advance for best torque operation, and remarkably high gross indicated that thermal efficiency of 52.63% can be achieved with a sufficiently low knock level and coefficient of variation of indicated mean effective pressure.

本文言語English
ページ(範囲)1421-1439
ページ数19
ジャーナルInternational Journal of Engine Research
22
5
DOI
出版ステータスPublished - 2021 5

ASJC Scopus subject areas

  • 自動車工学
  • 航空宇宙工学
  • 海洋工学
  • 機械工学

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