Control of PCCI Combustion using Physical and Chemical Characteristics of Mixed Fuel

Doshisha Univ. - Energy Conversion Research Center International Seminar on Recent Trend of Fuel Research for Next-Generation Clean Engines December 5th, 27 Control of PCCI Combustion using Physical and Chemical Characteristics of Mixed Fuel Doshisha Univ. Energy Conversion Research Center Postdoctoral fellow Yoshimitsu WADA

Contents Background Combustion Control Methodology using Mixed Fuel - simultaneous pursuit of high ignitability and high volatility - mixture formation control taking into account two-phase region Spray Characteristics of Mixed Fuel Combustion Characteristics of Mixed Fuel in CI Engine Conclusions

Progress in CI Engine Combustion PCCI combustion has the potential to be highly efficient and to produce low PM and NO x emissions. However, diesel fuel having low volatility, causes wall-wetting and poor mixture preparation. In addition, well-mixed mixture ignites simultaneously and the operation is limited by the steep pressure rise. Equivalence ratio [-] Low temp. rich combustion 7 *n-heptane, reaction time=1ms Ref) Kitamura, T. et al., Int. J. Engine Res., 22 6 5 4 3 2 Soot 25% 2% 15% 1% 5% 1% 5ppm Desirable path 1 5ppm PCCI NO 1 14 18 22 26 3 Temperature [K] MULDIC and MK combustion

Effect of Charge Heterogeneity on PCCI Combustion Steep combustion of HCCI is mitigated by employing charge heterogeneity Ref) Kumano, K. and Iida N., SAE Paper 24-1-192

Effect of Charge Heterogeneity on PCCI Combustion Experimental results Staged combustion event is achieved by employing partial fuel-stratification because the timing of hot ignition is sensitive to local φ. Computational results using CHEMKIN-Z Ref) Sjöberg, M. and Dec, J. E., SAE Paper 26-1-629 * Therefore, partial fuel-stratification is effective for fuels exhibiting two-stage ignition (LTR and HTR), such as gas oil.

Partial fuel-stratification is effective to reduce maximum pressure rise rate due to staged combustion event! Staged combustion event is achieved by fuels exhibiting two-stage ignition (LTR and HTR)! However... Fuels exhibiting two-stage ignition such as diesel fuel have low volatility How can we get fuels having high ignitability and high volatility??

Ignition Characteristics of Mixed Fuel Ignition delay τ [ms] 1.75 1.5 1.25 1..75 Single component fuel Mixed fuel of n-c 13 H 28 / n-c 5 H 12 Rapid Compression and Expansion Machine P inj =15MPa ρ a =17.8kg/m 3 T a =75K.5..25.5.75 Mole fraction of n-pentane 1. 13 11 9 7 Carbon number 5

Pressure-Temperature Diagram of Mixed Fuel Pressure Liquid Phase Bubble point curve Mixed Solution Two Phase Region Super Critical Region Dew point curve Low B.P. Component Temperature High B.P. Component Gas Phase

Flash Boiling Phenomena Nozzle internal flow Bubble growth = Evaporation Atomization Pressure Pressure T bub T T P a P a Temperature Temperature

Advantage of Flash Boiling for Early Timing Injections Fuel condition In-cylinder condition T bub1 Pressure T bub2 T bub3 Temperature Crank angle

Ambient and Fuel Conditions, plotted on P-T diagram of Mixed Fuel Test fuel : T n-tridecane + i-pentane f =31K 345K 38K 41K 435K 1.75 X ic5 =1. 1.5 T = T T ( p ) X ic5 =.8 Pressure [MPa] 1.25 1..75.5.25 bub f bub a T bub X ic5 =.. 32 36 4 44 48 Temperature [K]

Measured Spray Cone Angle as a Function of T bub (P inj =5MPa, d n =.2mm) Spray cone angle θ 1 [degree] 5 4 3 2 1 T f 31K 345K 38K 41K 435K to 2mm nozzle spray θ 1 = θ 1 +θ 1 d n -9-6 -3 3 6 9 12 Superheating from bubble point T bub [K] = θ 1 θ 1 A 1 A 1 A 1 A 1

Spray Images for each Superheating from Bubble Point (T a = 445K, ρ a =2.kg/m 3, P inj =5MPa, d n =.2mm) Axial distance from nozzle tip [mm] 22.5 45 67.5 9 T f =31K T f =345K T f =38K T f =41K T f =435K T bub [deg.] = -3.7 4.3 39.3 69.3 94.3 Time after Corrected Start of Injection:.45ms

Experimental Setup AVL 415S MEXA-15D Charge amplifier Surge tank Heated hose Injector Dynamometer Common rail ECU EDU PC Pressure transducer Engine Rotary encoder Supply pump Surge tank Resistance thermometer Electric Heater Laminar flow meter Dehumidified air

Effect of Superheating Degree and Injection Timings on Combustion Phasing (Included Spray Angle = 6deg.) Apparent heat release rate [J/deg.] Apparent heat release rate [J/deg.] 18 15 12 9 6 3 15 12 9 6 3 Higher superheating degree Early ignition Earlier injection timings late ignition θ inj =-7deg.CA ATDC θ inj =-8deg.CA ATDC θ inj =-9deg.CA ATDC -2-15 -1-5 TDC 5 φ=.3, ε =13 θ inj =-8deg.CA ATDC θ inj =-1deg.CA ATDC T f =31K, T bub = -3.7K T f =345K, T bub = 4.3K T f =38K, T bub = 39.3K T f =41K, T bub = 69.3K φ=.3, T f =41K, ε =13 Crank angle [deg. CA. ATDC]

Experimental Condition for the Case of Single Injection Fuel injection system Cooling System direct injection (common-rail) water cooled (353K) Bore Stroke [mm] 1 16 Compression ratio [-] 1. : 1 Intake temperature [K] varied Fuel n-c 13 H 28 + i-c 5 H 12 (X ic5 =.8) Fuel temperature T f 31, 41 Nozzle hole diameter [mm].2 (L n /d n = 4) Injection pressure [MPa] 5. Effective equivalence ratio φ eff [-].41 [K] Number of holes 4 Included spray angle [deg.] 1 5% burned crank angle 5.5 [deg. CA ATDC] (adjusted by intake air temperature)

Experimental Condition for the Case of Single Injection Fuel injection system Cooling System direct injection (common-rail) water cooled (353K) Bore Stroke [mm] 1 16 φ eff : Effective equivalence ratio calculated Compression from effective ratio injection quantity [-] Q eff,inj 1. : 1 Intake temperature [K] varied Q eff,inj : Injection quantity calculated from carbon balance method Fuel n-c 13 H 28 + i-c 5 H 12 (X ic5 =.8) Fuel temperature T f [K] 31, 41 Nozzle hole diameter [mm].2 (L n /d n = 4) Number of holes 4 Included spray angle [deg.] 1 Injection pressure [MPa] 5. Effective equivalence ratio φ eff [-].41 5% burned crank angle 5.5 [deg. CA ATDC] (adjusted by intake air temperature)

Relation among Two-Phase Region, In-Cylinder Pressure and Fuel Temperature 1. T f =31K T f =41K.8 Pressure [MPa].6.4.2 Start of injection [BTDC] 55deg.CA 6deg.CA 7deg.CA 8deg.CA 9deg.CA 1deg.CA 3 33 36 39 42 45 Temperature [K]

Combustion and Emissions Characteristics (Single Inj.) 4 35 3 Spray images at 8deg.CA BTDC Axial distance from nozzle exit [mm] Intake temp. [K] -1-9 -8-7 -6 Injection timing θ inj [deg.ca ATDC] 7.5 15 T f =31K T f =41K ( T bub = -3.7deg.) ( T bub = 69.3deg.) Amount of wall-wetting fuel [%] Fuel carbon into THC [%] NO x [g/g -fuel ] 18 15 12 9 6 3 1 8 6 4.75.5.25 T f =31K (W/O flash boiling) T f =41K (W/ flash boiling) -1-9 -8-7 -6-5 Injection timing θ inj [deg.ca ATDC] Fuel carbon into CO [%] 8 6 4 2

Combustion and Emissions Characteristics (Single Inj.) 4 35 3 Spray images at 8deg.CA BTDC Axial distance from nozzle exit [mm] Intake temp. [K] -1-9 -8-7 -6 Injection timing θ inj [deg.ca ATDC] Q wall wet 7.5 = Q real, inj Q Q real, inj eff, inj Amount of wall-wetting fuel [%] Fuel carbon into THC [%] NO x [g/g -fuel ] 18 15 12 9 6 3 1 8 6 4.75.5 T f =31K (W/O flash boiling) T f =41K (W/ flash boiling) Q real,inj : Measured injection quantity.25 15 Q eff,inj T f =31K : Injection quantity T f =41Kcalculated from -1-9 -8-7 -6-5 ( T bub = -3.7deg.) carbon balance ( T bub = 69.3deg.) method Injection timing θ inj [deg.ca ATDC] Fuel carbon into CO [%] 8 6 4 2

Experimental Condition for the Case of Two-Stage Injection Fuel n-c 13 H 28 + i-c 5 H 12 (X ic5 =.8) Fuel temperature T f 41 Compression ratio [-] 1. : 1 Intake temperature [K] 37 Nozzle hole diameter [mm].2 (L n /d n = 4) Number of holes 4 Injection pressure [MPa] 5. 1st injection timing [deg.ca ATDC] -8 Total supplied energy [J] 1335 (φ=.43 without EGR) [K] 5% burned crank angle [deg. CA ATDC] 3.75 (adjusted by EGR ratio)

Combustion and Emissions Characteristics (θ inj,1st =-8deg.CA ATDC, Q inj,2nd =3%) θ 5% is out-of-control EGR ratio [%] NO x [ppm] Maximum pressure rise rate [MPa/deg.] 3 2 1 2 15 1 5.7.6.5 1st injection only 1st injection only (NO X ) 1st injection only.4-5 -4-3 -2-1 2nd injection timing θ inj,2nd [deg.ca BTDC] after θ inj,2nd = -1deg..9.6.3 Smoke [FSN]

Combustion and Emissions Characteristics (θ inj,1st =-8deg.CA ATDC, Q inj,2nd =3%) EGR ratio [%] NO x [ppm] Maximum pressure rise rate [MPa/deg.] 3 2 1 2 15 1 5.7.6.5 1st injection only 1st injection only (NO X ) 1st injection only.4-5 -4-3 -2-1 2nd injection timing θ inj,2nd [deg.ca BTDC] θ 5% is out-of-control more NO x after θ inj,2nd = -1deg..9.6.3 Rich early ignition Lean late ignition less NO x Smoke [FSN]

Combustion and Emissions Characteristics (θ inj,1st =-8deg.CA ATDC, θ inj,2nd =-2deg.CA ATDC) EGR ratio [%] NO x [ppm] Maximum rate of pressure rise [MPa/deg.] 3 2 1 2 15 1 5.7.6.5.4 1st injection only 1st injection only (NO X ) 1st injection only 1 2 3 4 5 Percentage of 2nd injection quantity [%].9.6.3 Smoke [FSN]

Histories of Apparent Heat Release Rate (θ inj,1st =-8deg.CA ATDC, θ inj,2nd =-2deg.CA ATDC) Apparent heat release rate [J/deg.] Q inj,2nd =5% 2 Q inj,2nd =4% Q inj,2nd =1% Q inj,2nd =2% 15 Q inj,2nd =3% 1 5-15 -1-5 TDC 5 1 15 Crank angle [deg.ca ATDC]

Combustion and Emissions Characteristics (θ inj,1st =-8deg.CA ATDC, θ inj,2nd =-2deg.CA ATDC) Fuel carbon into THC [%] 3 2 1 1st injection only Fuel carbon into CO [%] Combustion efficiency [%] 3 2 1 99 96 93 1st injection only 1st injection only 1 2 3 4 5 Percentage of 2nd injection quantity [%]

Combustion and more Emissions HC, CO Characteristics (θ inj,1st =-8deg.CA ATDC, θ inj,2nd =-2deg.CA ATDC) Rich less CO Fuel carbon into THC [%] Fuel carbon into CO [%] Combustion efficiency [%] 3 2 1 3 2 1 99 96 93 1st injection only less HC, CO 1st injection only 1st injection only 1 2 3 4 5 Percentage of 2nd injection quantity [%] Reduction in 1st injection quantity Reduction in 1st injection quantity Lean more CO

Conclusions The flashing spray of mixed fuel is effective to reduce the amount of wall-wetting fuel, THC and CO emissions for early fuel injection. Mixed fuel consisting of high and low carbon number fuels exhibits active low temperature oxidation reaction and thus, this character makes it possible to mitigate the steep combustion. By choosing optimum ignitability of high carbon number fuel while keeping low temperature oxidation reactivity, further improvement of thermal efficiency would be achieved. (because compression ratio is set at 1 in this study) The multiple injection combined with flash boiling spray has a possibility of decreasing in both maximum pressure rise rate and NO X concentration.

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