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Investigation of dual-fuel compound HCCI combustion

Researchers from Shanghai Jiao Tong University report on the combustion and emission characteristics of dual-fuel compound homogeneous charge compression ignition (HCCI) combustion in a paper published in the International Journal of Engine Research.

They used n-heptane and oxygen-containing alcohols (e.g., ethanol) as the port-injection fuel and the in-cylinder direct-injection fuel, respectively. Among their findings:

  • Compound HCCI combustion with n-heptane port injection and alcohol direct injection exhibits a three-stage combustion process containing n-heptane low-temperature reactions, high-temperature reactions and alcohol combustion.

  • The crank angle position at which 10% of the mass fraction is burned is mainly dominated by the fuel heat value per cycle of premixed fuel, and is advanced with increasing the fuel heat value per cycle of premixed fuel and premixed ratio.

  • The crank angle position at which 50% of the mass fraction is burned shows remarkable sensitivity to the premixed ratio, and is advanced considerably as the premixed ratio and the fuel heat value per cycle of premixed fuel increase.

  • Burn duration increases with increasing total fuel heat value per cycle and fuel heat value per cycle of directly injected fuel.

  • Compound HCCI combustion could successfully reach the full load of the prototype engine, with indicated thermal efficiency very close to the prototype engine. However, CO and hydrocarbon emissions are relatively higher.

  • compound homogeneous charge compression ignition combustion with alcohol direct injection can reduce nitrogen oxide and soot emissions simultaneously. NOx emissions can be reduced below 100 ppm, and smoke opacity is below 15% at the full-load ranges.

  • With increasing oxygen content of directly injected fuels, soot emission of compound homogeneous charge compression ignition combustion decreases. Ethanol direct injection could make compound homogeneous charge compression ignition combustion nearly smoke free at the full-load ranges.

Resources

  • Zhen Huang, Libin Ji, Dong Han, Zheng Yang, and Xingcai Lu (2012) Experimental study on dual-fuel compound homogeneous charge compression ignition combustion. International Journal of Engine Research doi: 10.1177/1468087412440908

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