Cetane Number and Engine Speed Effects on Diesel HCCI Performance and Emissions

The effects of cetane number (CN) on homogeneous charge compression ignition (HCCI) performance and emissions were investigated in a single cylinder engine using intake air temperature for control. Blends of the diesel secondary reference fuels for cetane rating were used to obtain a CN range from 19 to 76. Sweeps of intake air temperature at a constant fueling were performed. Low CN fuels needed to be operated at higher intake temperatures than high CN fuels to achieve ignition. As the intake air temperature was reduced for a given fuel, the combustion phasing was retarded, and each fuel passed through a phasing point of maximum indicated mean effective pressure (IMEP). Early combustion phasing was required for the high CN fuels to prevent misfire, whereas the maximum IMEP for the lowest CN fuel occurred at a phasing 10 crank angle degrees (CAD) later. The high CN fuels exhibited a strong low temperature heat release (LTHR) event, accounting for more than 15% of the total heat release in some instances, while no LTHR was detected for fuels with CN ≤ 34. All of the fuels had comparable NOx emissions and pressure rise rates at their respective maximum IMEP timing, with NOx emissions below 6 ppm at 3.5 bar IMEP. At advanced combustion phasing, low CN fuels had significantly higher pressure rise rates and higher NOx emissions than the high CN fuels. At retarded phasing, the CO emissions for the high CN fuels were excessive, with a CO:UHC ratio of up to 8, while these remained <1 for low CN fuels. These results suggest that the products of LTHR, which are high in CO, are more sensitive to the quenching effects of cylinder expansion. Thus high CN fuels, which exhibit significant LTHR, require early combustion phasing, whereas low CN fuels can be retarded to later combustion phasing. Increasing engine speed had the effect of reducing the total LTHR. Further investigation showed that the LTHR rate is constant on a millisecond basis, so the effect of higher engine speed is to reduce the time allowed for the reaction without changing the rate of reaction.

[1]  Tanet Aroonsrisopon,et al.  Comparison of HCCI Operating Ranges for Combinations of Intake Temperature, Engine Speed and Fuel Composition , 2002 .

[2]  Pierre Duret,et al.  18 Gasoline CAI and Diesel HCCI: the Way towards Zero Emission with Major Engine and Fuel Technology Challenges , 2002 .

[3]  Rolf D. Reitz,et al.  Experimental Investigation of Direct Injection-Gasoline for Premixed Compression Ignited Combustion Phasing Control , 2002 .

[4]  Bengt Johansson,et al.  Influence of Mixture Quality on Homogeneous Charge Compression Ignition , 1998 .

[5]  Bengt Johansson,et al.  Demonstrating the Multi Fuel Capability of a Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio , 1999 .

[6]  R. Yetter,et al.  Inhibition of moist carbon monoxide oxidation by trace amounts of hydrocarbons , 1992 .

[7]  Fabian Mauss,et al.  Supercharged Homogeneous Charge Compression Ignition , 1998 .

[8]  Thomas W. Ryan,et al.  Homogeneous Charge Compression Ignition (HCCI) of Diesel Fuel , 1997 .

[9]  Tanet Aroonsrisopon,et al.  An Investigation Into the Effect of Fuel Composition on HCCI Combustion Characteristics , 2002 .

[10]  Koji Hiraya,et al.  A Study on Gasoline Fueled Compression Ignition Engine ∼ A Trial of Operation Region Expansion ∼ , 2002 .

[11]  Richard Stone,et al.  Introduction to Internal Combustion Engines , 1985, Internal Combustion Engines.

[12]  William R. Leppard,et al.  The chemical origin of fuel octane sensitivity , 1990 .

[13]  C. Westbrook,et al.  A Comprehensive Modeling Study of n-Heptane Oxidation , 1998 .

[14]  Hua Zhao,et al.  Dilution Effects on the Controlled Auto-Ignition (CAI) Combustion of Hydrocarbon and Alcohol Fuels , 2001 .

[15]  Makoto Kaneko,et al.  A Study on Homogeneous Charge Compression Ignition Gasoline Engines , 2003 .

[16]  Nicolas Jeuland,et al.  Engine and Fuel Related Issues of Gasoline CAI (Controlled Auto-Ignition) Combustion , 2003 .

[17]  Gen Shibata,et al.  Correlation of Low Temperature Heat Release With Fuel Composition and HCCI Engine Combustion , 2005 .

[18]  John E. Dec,et al.  Isolating the Effects of Fuel Chemistry on Combustion Phasing in an HCCI Engine and the Potential of Fuel Stratification for Ignition Control , 2004 .

[19]  Bengt Johansson,et al.  Homogeneous Charge Compression Ignition (HCCI) Using Isooctane, Ethanol and Natural Gas - A Comparison with Spark Ignition Operation , 1997 .

[20]  Wei Chen,et al.  A fundamental study on the control of the HCCI combustion and emissions by fuel design concept combined with controllable EGR. Part 2. Effect of operating conditions and EGR on HCCI combustion , 2005 .

[21]  Wei Chen,et al.  A fundamental study on the control of the HCCI combustion and emissions by fuel design concept combined with controllable EGR. Part 1. The basic characteristics of HCCI combustion , 2005 .

[22]  Song-Charng Kong,et al.  Application of detailed chemistry and CFD for predicting direct injection HCCI engine combustion and emissions , 2002 .

[23]  Fuquan Zhao,et al.  Homogeneous charge compression ignition (HCCI) engines : key research and development issues , 2003 .