Smoothing HCCI Heat Release with Vaporization-Cooling-Induced Thermal Stratification using Ethanol

Ethanol and ethanol/gasoline blends are being widely considered as alternative fuels for light-duty automotive applications. At the same time, HCCI combustion has the potential to provide high efficiency and ultra-low exhaust emissions. However, the application of HCCI is typically limited to low and moderate loads because of unacceptably high heat-release rates (HRR) at higher fueling rates. This work investigates the potential of lowering the HCCI HRR at high loads by using partial fuel stratification to increase the in-cylinder thermal stratification. This strategy is based on ethanol's high heat of vaporization combined with its true single-stage ignition characteristics. Using partial fuel stratification, the strong fuel-vaporization cooling produces thermal stratification due to variations in the amount of fuel vaporization in different parts of the combustion chamber. The low sensitivity of the autoignition reactions to variations of the local fuel concentration allows the temperature variations to govern the combustion event. This results in a sequential autoignition event from leaner and hotter zones to richer and colder zones, lowering the overall combustion rate compared to operation with a uniform fuel/air mixture. The amount of partial fuel stratification was varied by adjusting the fraction of fuel injected late to produce stratification, and also by changingmore » the timing of the late injection. The experiments show that a combination of 60-70% premixed charge and injection of 30-40 % of the fuel at 80{sup o}CA before TDC is effective for smoothing the HRR. With CA50 held fixed, this increases the burn duration by 55% and reduces the maximum pressure-rise rate by 40%. Combustion stability remains high but engine-out NO{sub x} has to be monitored carefully. For operation with strong reduction of the peak HRR, ISNO{sub x} rises to around 0.20 g/kWh for an IMEP{sub g} of 440 kPa. The single-cylinder HCCI research engine was operated naturally aspirated without EGR at 1200 rpm, and had low residual level using a CR = 14 piston.« less

[1]  John E. Dec,et al.  Ethanol Autoignition Characteristics and HCCI Performance for Wide Ranges of Engine Speed, Load and Boost , 2010 .

[2]  Hakan Yilmaz,et al.  Parameter Optimization of a Turbo Charged Direct Injection Flex Fuel SI Engine , 2009 .

[3]  John E. Dec,et al.  An investigation into lowest acceptable combustion temperatures for hydrocarbon fuels in HCCI engines , 2005 .

[4]  Roald N. Leif,et al.  Detailed HCCI Exhaust Speciation and the Sources of Hydrocarbon and Oxygenated Hydrocarbon Emissions. , 2008 .

[5]  John E. Dec,et al.  Effects of engine speed, fueling rate, and combustion phasing on the thermal stratification required to limit HCCI knocking intensity , 2005 .

[6]  Nicholas P. Cernansky,et al.  Potential of Thermal Stratification and Combustion Retard for Reducing Pressure-Rise Rates in HCCI Engines, Based on Multi-Zone Modeling and Experiments , 2005 .

[7]  William Cannella,et al.  Partial Fuel Stratification to Control HCCI Heat Release Rates: Fuel Composition and Other Factors Affecting Pre-Ignition Reactions of Two-Stage Ignition Fuels , 2011 .

[8]  I. Denbratt,et al.  A study of the influence of exhaust gas recirculation and stoichiometry on the heat release in the end-gas prior to knock using rotational coherent anti-Stokes-Raman spectroscopy thermometry , 2002 .

[9]  John E. Dec,et al.  An Investigation of the Relationship Between Measured Intake Temperature, BDC Temperature, and Combustion Phasing for Premixed and DI HCCI Engines , 2004 .

[10]  John E. Dec,et al.  Spectroscopic and chemical-kinetic analysis of the phases of HCCI autoignition and combustion for single- and two-stage ignition fuels , 2008 .

[11]  N. Marinov,et al.  A detailed chemical kinetic model for high temperature ethanol oxidation , 1999 .

[12]  William J. Pitz,et al.  Detailed Kinetic Modeling of Low-Temperature Heat Release for PRF Fuels in an HCCI Engine , 2009 .

[13]  Takayuki Fuyuto,et al.  Dual-Fuel PCI Combustion Controlled by In-Cylinder Stratification of Ignitability , 2006 .

[14]  John E. Dec,et al.  Comparing late-cycle autoignition stability for single- and two-stage ignition fuels in HCCI engines , 2007 .

[15]  Dennis N. Assanis,et al.  Comparing Enhanced Natural Thermal Stratification Against Retarded Combustion Phasing for Smoothing of HCCI Heat-Release Rates , 2004 .

[16]  Daniel L. Flowers,et al.  Improving Ethanol Life Cycle Energy Efficiency by Direct Utilization of Wet Ethanol in HCCI Engines , 2007 .

[17]  John E. Dec,et al.  Effects of EGR and its constituents on HCCI autoignition of ethanol , 2011 .

[18]  John E. Dec,et al.  Smoothing HCCI Heat-Release Rates Using Partial Fuel Stratification with Two-Stage Ignition Fuels , 2006 .

[19]  John E. Dec,et al.  Characterizing the Development of Thermal Stratification in an HCCI Engine Using Planar-Imaging Thermometry , 2009 .

[20]  Yukihisa Yamaya,et al.  Premixed Compression Ignition of Formaldehyde-Doped Lean Butane/Air Mixtures in a Wide Range of Temperature , 2004 .

[21]  W. Anderson,et al.  Understanding the Thermodynamics of Direct Injection Spark Ignition (DISI) Combustion Systems: An Analytical and Experimental Investigation , 1996 .

[22]  John E. Dec,et al.  Boosted HCCI - Controlling Pressure-Rise Rates for Performance Improvements using Partial Fuel Stratification with Conventional Gasoline , 2011 .

[23]  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 .

[24]  D. Splitter,et al.  Reactivity Controlled Compression Ignition (RCCI) Heavy-Duty Engine Operation at Mid-and High-Loads with Conventional and Alternative Fuels , 2011 .

[25]  J. Dec,et al.  Fuel Stratification for Low-Load HCCI Combustion: Performance & Fuel-PLIF Measurements , 2007 .

[26]  John E. Dec,et al.  Tailoring HCCI heat-release rates with partial fuel stratification: Comparison of two-stage and single-stage-ignition fuels , 2011 .

[27]  John E. Dec,et al.  Boosted HCCI for high power without engine knock and with ultra-low NOx emissions - Using conventional gasoline , 2010 .

[28]  John E. Dec,et al.  A Parametric Study of HCCI Combustion - the Sources of Emissions at Low Loads and the Effects of GDI Fuel Injection , 2003 .