Knock Prevention by Retarded Injection with Ultra-High Pressure and Fuel Injector Nozzle Development

Authors

Dr. Peter Richardson, Dr. Jiayi Gu, Dr. Gianluca Di Liberto, DENSO International Europe, Coventry;
Kayoko Kimoto, Kenji Aoyagi, Hitoshi Shibata, DENSO CORPORATION, Kariya, Japan

Summary

With the increasing trend for higher compression ratio engines to achieve improved thermal efficiency comes the challenge for robust knock prevention strategies. This research aims to investigate the effect of retarded injection on knock prevention using ultra-high pressure injection. Retarded Start Of Injection (SOI) allows suppression of excessive oxidation reaction, via fuel cooling, shortened high temperature exposure time of the fuel and in-cylinder turbulence formation.

To achieve the benefits of retarded injection, rapid formation of a stable and homogeneous air-fuel mixture to achieve optimum combustion, as well as avoiding wall impingement of the fuel spray is required. Prompt mixture formation with retarded injection promotes fast and even flame propagation to achieve completion of combustion before auto-ignition occurs in the end-gas. Spray impingement should be avoided to maximise the energy available to increase turbulence and support mixture formation. DENSO improved nozzle technology, designed for high pressure usage, leads to superior spray atomisation, break-up and improved spray homogeneity by promoting air entrainment, resulting in lower impingement and improved mixture homogeneity.

Computational and experimental investigations were performed to evaluate the effect of retarded injection on mixture formation and knock prevention. Engine results with retarded SOI showed that the centre of combustion could be advanced by up to 8CA compared to intake injection. This resulted in up to 7 % Indicated Specific Fuel Consumption (ISFC) improvement. By optimising nozzle technology and injection control, further improvements in combustion can be expected.

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