International Journal of Automotive Technology

, Volume 19, Issue 4, pp 605–614 | Cite as

Effect of Charge Density on Spray Characteristics, Combustion Process, and Emissions of Heavy-Duty Diesel Engines

  • Bin Yang Wu
  • Qiang Zhan
  • Xiao Yang Yu
  • Wen Yu Gu
  • Min Zhang
  • Wanhua Su


In-cylinder charge density at top dead center is an important parameter of diesel engines and is influenced by intake pressure, intake temperature, and compression ratio. The effects of charge density on fuel spray, combustion process, and emissions were investigated by using a constant volume bomb and a heavy-duty diesel engine. Spray development resistance increased with the increase of the charge density in the constant volume bomb. It was found that short spray penetration was accompanied by a large spray cone angle in the former stage with high charge density. However, the equivalence ratio was lowered and the degree of homogeneity of the mixture was increased in the later stage owing to the rapid interaction of fuel and gas at a high mixing rate. Combining the first law of thermodynamics and the second law of thermodynamics for analysis, as the charge density increased, the gross indicated thermal efficiency (ITEg) was improved. However, pumping loss had to be considered with higher charge density. Under this condition, the brake thermal efficiency (BTE) trend was increased initially and decreased subsequently. Under high-load operation (1200 r/min BMEP, 2.0 MPa), the minimum charge density value of 44.8 kg/m3 was found to be reasonable. This charge density was suitable for combustion and brought about minimum exhaust energy and trade-off emissions. Moreover, by analyzing two operation conditions in terms of the maximum BTE with the Miller and the conventional cycles, compression temperature and combustion temperature were reduced in the Miller cycle with the charge density 44.8 kg/m3. A high Cp/Cv could improve the cylinder exergy/power conversion process by its positive effect of increasing the specific heat ratio. Owing to the interaction between a high Cp/Cv and exergy loss to heat transfer, the condition with the minimal charge density could produce more piston work.

Key Words

Charge density Spray character Thermal efficiency Miller cycle Combustion process 




brake mean effective pressure


brake thermal efficiency


carbon monoxide


exhaust gas recirculation


hydrocarbon compounds


homogeneous charge compression ignition


indicated mean effective pressure


intake valve closing timing


gross indicated thermal efficiency


late intake valve closing


low temperature combustion


equivalence ratio


nitrogen oxides


partial premix combustion


rate of heat release


reaction controlled compression ignition


top dead center


variable geometry turbine







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Copyright information

© The Korean Society of Automotive Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Bin Yang Wu
    • 1
  • Qiang Zhan
    • 2
  • Xiao Yang Yu
    • 1
  • Wen Yu Gu
    • 1
  • Min Zhang
    • 1
  • Wanhua Su
    • 1
  1. 1.State Key Laboratory of EnginesTianjin UniversityTianjinChina
  2. 2.Engine Research InstituteWeichai Power Co., LtdWeifangChina

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