Premixed combustion of blends of n-heptane and gasoline in a rapid compression machine

Transcription

1 7 th Annual CE-CERT-SJTU Student Symposium Premixed combustion of blends of n-heptane and gasoline in a rapid compression machine Yang Zheng, Han Dong,Guang Huanyu,Lu Xingcai, Huang Zheng

2 EI NOx (g/kg fuel) Soot (FSN) EI NOx (g/kg fuel) Soot (FSN) EI NOx (g/kg fuel) Soot (FSN) Background Ignition delay time is an important factor of low temperature combustion in diesel engine. Extending the fuel and gas mixing time before ignition can reduce the local equivalence ratio to control the soot emissions. The premixed low-temperature combustion of blends of diesel and gasoline might be a way to solve the NOx-soot trade off problem. The key point is the fuel design and the management NOx Soot G NOx Soot NOx Soot Intake Oxygen Concentration (%) Intake Oxygen Concentration (%) Intake Oxygen Concentration (%) Ref: Dong Han, Andrew M. Ickes, Stanislav V. Bohac, Zhen Huang, Dennis N. Assanis. Premixed lowtemperature combustion of blends of diesel and gasoline in a high speed compression ignition engine. Proceedings of the combustion institute,, 33 (22):

3 Introduction to RCM

4 The experimental method PC Æø¹ Þ Æø¹ Þ Ñ ¹Æø» ú Conditions:T = 298±1 K,P =.1 MPa ² ɼ N 2 O 2 CO 2» ìæøê Ò amp È ¼É ÕÊ Ò Õ æ Õ± à Rapid compression machine Fuel:gasoline /n-heptane premixed Gas: homogeneous mixture The proportion of gasoline : % -% Compression ratio: Fuel air equivalence ratio : The proportion of CO2: %, 4%, 8%

5 Basic parameters of RCM Compression ratio 8-3 Compression stroke(mm) Compression time(ms) ~6 Clearance height(mm) Bore(mm) Driving pressure (MPa)

6 Rapid Compression machine Drive system PC Control system t ank card amp combust i on room t ank mi xi ng chamber Gas supply system N 2 O 2 CO 2 vacuum pump compr essor >99.99% >99.99% >99.99%

7 Typical experimental results and reproducibility Pressure( bar) 25 Dummy run-1 Dummy run-2 Combustion-1 Combustion-2 Combustion Driven Pressure P=.232Mpa CR=11.28 Test Fuel:n-heptane equivalent ratio:.2 T=295K Time( ms)

8 Cylinder Pressure (MPa) The parameter definition of ignition process Pressure Rising Rate (MPa/s) 3 P PRR TDC τ1 τ2 1st stage ignition Time (s) Peak Pressure Location 2nd stage ignition TDC:Starting point The first stage ignition delay time : t1 The second stage ignition delay time :t2 Peak pressure location Pressure trace illustrating the definitions of the ignition delay G,Φ =.4,CR=12.5 3

9 Cylinder Pressure (MPa) Experimental pressure history for various mixtures G G7 G As the gasoline proportion increase, the 3.5 pressure curve shows an 3. apparent two stage 2.5 Gasoline Increases pressure rise Time after compression (ms) The pressure history of different fuels (Φ =.4,CR =12.5)

10 Maximum Pressure Rising Rate (MPa/s) The gasoline proportion effects on combustion Ignition Delay (ms) st Stage 2nd Stage With increased gasoline proportion, both the maximum pressure rising rates of the two stages decrease st Stage ID 2nd Stage ID Overall ID Gasoline Percentage (%) Adding gasoline to the n- heptane can effectively increase the fuel ignition delay,and in most cases,the first stage ignition delay time is slightly longer than the second stage Gasoline Percentage (%)

11 Overall Ignition Delay (ms) The compression ratio effects on combustion 1st Stage Ignition Delay (ms) 2nd Stage Ignition Delay (ms) G G7 G Knock Limit Φ =.4 Both two stage ignition delay times increase with reduced compression ratio 12 For a given compression ratio,adding gasoline increases the fuel ignition delay 8 time. 8 6 G7 G G7 G 4 3 G7 G

12 Peak Pressure (MPa) The compression ratio effects on combustion Peak Pressure Rising Rate (MPa/s) Peak Pressure Rising Rate (MPa/s) G7 G 8 1st Stage Heat Release G G7 G 15 2nd Stage Heat Release G7 G With increased compression ratio, the peak pressure gradually increased. For a given compression ratio,the increased gasoline proportion can make a significant reduction in peak pressure. The peak pressure rise rates of two stages show similar trends with the changes in compression ratio and fuel components. The maximum pressure rise rate of the second stage is much higher than the first stage under high compression ratio conditions

13 Overall Ignition Delay (ms) 1st Stage Ignition Delay (ms) 2nd Stage Ignition Delay (ms) The fuel air equivalence ratio effects on combustion Φ=.3 Φ=.4 Φ= Φ=.3 Φ=.4 Φ= Compressipon Ratio Compressipon Ratio Φ=.3 Φ=.4 Φ= Compressipon Ratio The first stage ignition delay time increases slightly with the rising fuel air equivalence ratio. The second stage ignition delay time reduces with the rising fuel air equivalence ratio.

14 Overall Ignition Delay (ms) 1st Stage Ignition Delay (ms) 2nd Stage Ignition Delay (ms) The CO2 concentration effects on combustion % CO 2 4% CO 2 8% CO % CO 2 4% CO 2 8% CO % CO 2 4% CO 2 8% CO , Φ =.5 Both two stage ignition delay times increase with the rising CO2 concentration. The increased CO2 concentration mainly extends the first stage of the ignition delay time, while the impact on the second stage ignition delay time is relatively fair

15 Peak Pressure (MPa) Peak Pressure Rising Rate (MPa/s) The CO2 concentration effects on combustion Peak Pressure Rising Rate (MPa/s) 15 % CO 2 4% CO 2 8% CO 2 1st Stage Heat Release 3 % CO 2 4% CO 2 8% CO 2 2nd Stage Heat Release , Φ = % CO 2 4% CO 2 8% CO 2 The peak pressure and both two stage peak pressure rise rates decrease with the rising CO2 concentration. When CO2 concentration is high, the impact of increasing CO2 concentrations is not significant.

16 Conclusion 31 Adding gasoline into n-heptane leads to an apparent two stage rise in combustion pressure curve. It can effectively reduce the maximum pressure rise rates of the two stages, and extend their ignition delay times. 2 The fuel air equivalence ratio affects the two-stage ignition delay times in different ways.the first stage ignition delay time increases slightly while the second stage ignition delay time decreases with the rising fuel air equivalence ratio. The increased CO2 concentration could decrease the peak pressure and both two stage peak pressure rise rates,but effectively extend the ignition delays of two combustion stages.

17 Thanks The authors appreciate the financial support from natural science foundation key project