University of Wisconsin - Engine Research Center Slide 1 Homogeneous Charge Compression Ignition (HCCI) Combustion Control using Gasoline/Diesel Fuel Blends Ritwik Athalye, George Chandler, Sibin Kurunthottikkal Philip, Chandra Shekhar Vishwanadha ME 769 Project Presentation May 5 th, 2015

University of Wisconsin - Engine Research Center Slide 2Overview Introduction Motivation Objectives Initial Study  Assumptions Results  Engine Speed  Equivalence Ratio  Fuel-Blending  Exhaust Gas Recirculation Discussion  Combustion Phasing (CA50)  Peak Pressure Rise Rate  Emissions  Indicated Work and GIE Optimization Conclusions Further Studies

University of Wisconsin - Engine Research Center Slide 3 Introduction Stricter emission regulations and demand for higher efficiency in IC Engines Development of new combustion modes with the aim of reducing fuel consumption and emissions HCCI : a promising alternative to SI and CI combustion Mainly driven by chemical kinetics of hydrocarbon oxidation chemistry leading to auto-ignition of homogeneous charge Potential to achieve high efficiency and ultra-low NOx and soot emissions (uniformly lean LTC) UW ERC Website

University of Wisconsin - Engine Research Center Slide 4 Motivation Practical issues with combustion control over a wide speed- load operating range Combustion phasing Controlling the low temperature heat release over range of engine speeds Controlling heat release rate and peak pressure rise rate Incomplete combustion in low load and high load regimes (lean and rich combustion) Emissions such as CO and UHC

University of Wisconsin - Engine Research Center Slide 5 Objectives To investigate the Gasoline/Diesel HCCI combustion over a range of speeds and loads using CHEMKIN kinetic solver Perform parametric studies by varying the engine operating conditions to analyze their effects on the combustion process Operating Conditions: engine speed, equivalence ratio (load), gasoline/diesel fuel-blend, and externally cooled EGR Effects: combustion phasing (CA50), heat release rate, peak pressure rise rate, emissions, indicated work, gross indicated efficiency Complete iterative optimization study at problematic operation condition

University of Wisconsin - Engine Research Center Slide 6 Assumptions: Reactor Constants Used ‘IC Engine’ reactor model in Chemkin  Engine geometries and some initial conditions were taken from Sandia National Lab HCCI experiments (HW #3)  Woschni heat transfer model was implemented in simulations  Reduced initial (IVC) temperature to more realistic HCCI value  Used ‘ERC Reduced PRF Mechanism’ for gasoline/diesel combustion (73 species, 295 reactions) Added NOx mechanisms (4 species, 13 reactions)

University of Wisconsin - Engine Research Center Slide 7 Assumptions: Reactor Variables ‘baseline’ case of literature-supported typical HCCI combustion parameters was created  Assumed parameters would be varied individually in study Engine Speeds: 600, 1200, 2000, 2500 [rpm] Equivalence Ratio: 0.1, 0.2, 0.3, 0.4, 0.5 (Φ) Gasoline Volume Percent: 0, 25, 50, 75, 100 [%] Exhaust Gas Recirculation by Volume: 0, 10, 20, 30, 40, 50 [%]

University of Wisconsin - Engine Research Center Slide 8 Results: Engine Speed With 2-stage auto-ignition fuels, the low temperature heat release (LTHR) is a critical factor in combustion phasing and high temperature heat release (HTHR) Cool flame reactions occur at similar times for all engine speeds, meaning timing of LTHR is highly dependent on engine speed LTHR decreases with increasing speed, delaying and lowering the rate of the HTHR In the highest speed case, LTHR is so trivial and delayed that the HTHR does not take place, and misfire occurs Sjöberg et al, 2007, Aroonsrisopon et al, 2002

University of Wisconsin - Engine Research Center Slide 9 Results: Equivalence Ratio Equivalence ratio can be used to control engine load Increasing equivalence ratio increases peak pressure LTHR scales proportionally with equivalence ratio Strong correlation between magnitude of LTHR and phasing as well as magnitude of HTHR Lean combustion limit was found around Φ=0.2 Increasing equivalence ratio advanced combustion and increased the heat release rate of the HTHR Babiker et al, 2010

University of Wisconsin - Engine Research Center Slide 10 Results: Fuel-Blending Diesel fuel plays an important role in the mixture, since it is much more prone to auto-ignition than gasoline Higher diesel percentage advances HTHR likely due to the increase in magnitude of LTHR Pure gasoline case does not ignite, likely due to its low reactivity and difficulty auto-igniting Zhong et al, 2005

University of Wisconsin - Engine Research Center Slide 11 Results: Exhaust Gas Recirculation External cooled exhaust gas recirculation (EGR) was applied as volume percent, where there was no influence on mixture temperature at IVC Increase in EGR delays ignition timing, lowers peak pressure, slows and lowers heat release rate  Due to decrease in apparent equivalence ratio  Due to increase in mixture specific heat High values of EGR (>30%) resulted in incomplete combustion Nakano et al, 2000 Charalambides, 2013

University of Wisconsin - Engine Research Center Slide 12 Discussion: Combustion Phasing (CA50) Increasingly rich combustion advances CA50 likely due to the proportional increase in the LTHR magnitude heating mixture for easier HTHR Increasing engine speed retards CA50, even to the point of misfiring Increasing gasoline volume percentage retards CA50, due to lowering mixture reactivity and inhibiting auto-ignition Nakano et al, 2000 Increasing cooled EGR retards combustion due to leaning and increased heat capacity effects  Realistically with internal EGR, mixture temperature increases with EGR. This works to advance CA50

University of Wisconsin - Engine Research Center Slide 13 Discussion: Peak Pressure Rise Rate (PPRR) Ghafouri et al, 2014 Nakano et al, 2000 Increasing equivalence ratio promotes higher peak pressure and PPRR due to higher energy input  Quickly exceeds acceptable values Faster engine speeds tend to lower PPRR due to shortening of LTHR Increasing gasoline content in mixture does not have strong correlation with PPRR Increasing EGR lowers PPRR due to larger mixture heat capacity and leaning effects

University of Wisconsin - Engine Research Center Slide 14 Discussion: Emissions Since a reduced mechanism and simplified combustion model was used, emission data may be generally unrealistic High unburned hydrocarbon (UHC) and CO levels were seen where misfires occurred Higher NOx levels generally occurred in cases where high combustion temperatures and HRR were reached  ie. Φ=0.4 and 0.5 cases

University of Wisconsin - Engine Research Center Slide 15 Discussion: Indicated Work and GIE As expected, large proportionality between fuel energy in mixture and indicated work Also expected, cases with a CA50 closer to TDC had higher Gross Indicated Efficiency (GIE) GIE can be used in determining operational limits of engine

University of Wisconsin - Engine Research Center Slide 16 Optimization: High Load Case Low Speed Case High Load Operation Issues: EGR is one of the ways to mitigate the PPRR; however, it would reduce the fuel input and hence the load on the engine. Low Speed Operation Issues:  Issues with low speed mode such as early ignition and high PPRR  In order to delay ignition, a higher gasoline mixture is used  In order to reduce PPRR, some EGR is introduced This lowers indicated work significantly

University of Wisconsin - Engine Research Center Slide 17 Conclusions Gasoline/diesel fuel blends, which inherently have dissimilar reactivities, can be used effectively to phase HCCI combustion in moderate engine speeds ( rpm) and medium loads The LTHR is particularly important to combustion phasing and heat release rate with gasoline/diesel fuel blends  Diesel accounted for larger portion of LTHR  Large LTHR can serve to advance the HTHR HCCI is limited in the high load condition due to PPRR and resulting knock risk HCCI combustion achieved high efficiency and low NOx formation on account of low temperature combustion

University of Wisconsin - Engine Research Center Slide 18 Further Studies Use of EGR with boosted operation Investigation of EGR while maintaining constant fuel amount EGR effects on IVC temperature Variable Compression Ratio

University of Wisconsin - Engine Research Center Slide 19 Thank You!