Investigation of combustion characteristics of a diesel engine fueled with DME-biodiesel blends

Transcription

1 Investigation of combustion characteristics of a diesel engine fueled with DME-biodiesel blends Qiao Xinqi School of Mechanical Engineering, China

2 Outline 1. Introduction 2. Research approach 3. Experimental apparatus 4. Results and discussion 5. Conclusions

3 1. Introduction DME Low viscosity and surface tension Blended Biodiesel High viscosity and surface tension Proper Lubricity, atomization, heat value and combustion, performance.

4 2. Research approach Combustion experiment for measuring engine performance Heat release analysis In-cylinder pressure pressure rise rate In-cylinder temperature Heat release rate DWT(discrete wavelet transform) analysis Amplitude of subsignal Wavelet relative energy

5 DWT analysis Table.1 Frequency band of each layer Wavelet layer Frequency band (khz) 1 ( D1) ( D2 ) ( D3 ) ( D4 ) ( A4 ) With Daubechies 10 as wavelet, in-cylinder pressure is decomposed into four layers that contain four details D1, D2, D3, D4 and an approximation A4.

6 To quantify intensity of pressure oscillation The amplitude of pressure subsignal p Dj at layer j is defined as half of the difference between its maximum and minimum. Wavelet relative energy R j at layer j is defined as the ratio of detail energy Ej of the in-cylinder pressure signal to the total detail energy E of the four layers [14], expressed as R j E j E j 4 E E j 1 j N j E j d j k 1, k 2 Where, k is an integer as the coefficient ordinal number, and Nj the number of detail coefficient dj,k at layer j.

7 3. Experimental apparatus Table 2. Specifications of test diesel engine bore / stroke / mm 135/145 Compression ratio 16.5 Rated speed /(r min-1) 1500 Rated power/ kw 29.4 Fuel delivery advance angle / oca BTDC 28 Nozzle orifice number diameter (mm) 4 5 Nozzle opening pressure 19 In view of low heat value and excellent atomization of DME, for blends containing more than 50% of DME, nozzle orifice number diameter is changed from 4 5 mm to mm, and nozzle opening pressure is decreased from 19 to 15 MPa to increase fuel injection supply. Table 3. Properties of test biodiesel and DME Parameter biodiesel DME Density g/cm 3 (20 C) Kinematic viscosity mm 2 /s(40 C) Surface tension kg/s 2 (40 C) Low heat value MJ/kg Cetane number 51 55~66

8 p Heat Release Rate / J/ o CA p Heat Release Rate / J/ o CA 7 th Asian DME Conference 4. Results and discussion BMEP=0.135MPa BMEP=7MPa Effect of DME proportion on in-cylinder pressure and heat release rate With the increase of DME proportion, the peak in-cylinder pressure decreases with retarded peak pressure phase. But is the exception. At two BMEP, increased DME proportion causes reduced premixed combustion, the peak heat release rate and retarded phasing, but increased diffusive combustion and the peak heat release in diffusive combustion increases.

9 Pressure Rise Rate /( MPa/ o CA) Pressure Rise Rate /( MPa/ o CA) 7 th Asian DME Conference BMEP=0.135MPa BMEP=7MPa Effect of DME proportion on in-cylinder pressure rise rate Increased DME proportion reduces the peak pressure rise rate and retards phase, thus producing a soft engine operation.

10 In-Cylinder Temperature / K In-Cylinder Temperature / K 7 th Asian DME Conference 1400 BMEP=0.135MPa BMEP=7MPa Effect of DME proportion on in-cylinder temperature With increased DME proportion, the peak in-cylinder temperature decreases, and their phase retards.

11 Smoke Opacity / % BMEP NOx / BMEP Effect of DME proportion on smoke emissions and NOx emissions As BMEP increases, smoke emission increases, but changes little for blended fuels containing more than 50% of DME. At the same BMEP, the increased DME proportion reduces smoke emissions, especially at high BMEP. NOx emissions increase with increased BMEP At the same BMEP, NOx emissions decrease with increased DME proportion.

12 p D2 p D1 p D2 p D p D2 p D1 p D2 p D BMEP=0.135 MPa Wavelet decomposition of in-cylinder pressure

13 p D2 p D p D2 p D BMEP=0.135 MPa - p D2 p D Wavelet decomposition of in-cylinder pressure

14 p D2 p D p D2 p D p D2 p D BMEP=7 MPa Wavelet decomposition of in-cylinder pressure

15 Amplitude Amplitude 7 th Asian DME Conference 0.4 p D1 BMEP=0.135MPa 0.4 p D1 BMEP=7MPa p D2 p D Effect of DME proportion on amplitude of subsignal At MPa BMEP, the amplitude of is obviously greater than those of p D1, p D2 and. With decreased DME proportion from DME 100 to,, the amplitude of gradually increases. As fuel changes from to, the amplitude of decreases, but the amplitude of increases. As changes to, the amplitude of and both increase.

16 Wavelet Relative Energy / % D1 D3 D2 D4 Wavelet Relative Energy / % D1 D3 D2 D4 0 0 BMEP=0.135 MPa BMEP=0.135 MPa Wavelet relative energy of in-cylinder pressure with blend fuels The wavelet relative energy at detail D4 is the largest for all five test fuels. With increased DME proportion in fuel blends, the relative energy at D4 increases, with a reduction of relative energy at D1, D2 and D3. As BMEP increases from 0.135MPa to 7MPa, the relative energy at D4 is still the largest for all five test fuels, relative energy at others are still small.

17 PRA/( MPa/ o CA 2 ) PRR/( MPa/ o CA) HRR/( J/ o CA) 7 th Asian DME Conference p D2 p D Relation of heat release analysis and wavelet analysis Just as the peak heat release rate, pressure rise rate and pressure rise acceleration, so the peak amplitudes of subsignals at four layers are located within premixed combustion phase. The peaks of subsignals represent pressure oscillation of premixed combustion.

18 5. Conclusions 1 With the increase of DME proportion, the peak in-cylinder pressure and pressure rise rate decrease with retarded phase, thus producing a soft engine operation. A two-stage combustion of DME-biodiesel blends is exhibited, including premixed combustion and diffusive combustion. Increased DME proportion causes reduced premixed combustion, the peak heat release rate and retarded phasing, but increased diffusive combustion and the peak heat release in diffusive combustion increases. 2 As BMEP increases, smoke emissions increase, but change little for blended fuels containing more than 50% of DME. At the same BMEP, the increased DME proportion reduces smoke emissions, especially at high BMEP. NOx emissions increases with increased BMEP, and at the same BMEP, NOx emissions decrease with increased DME proportion. 3 The curves of and change slowly with relatively large oscillation amplitude, but rapidly change of p D1 and p D2 with small oscillation amplitude. The heat release analysis is associated with in-cylinder pressure four-layer wavelet analysis of blended fuels. Just as the peak heat release rate, pressure rise rate and pressure rise acceleration, so the peak amplitudes of subsignals at four layers are located within premixed combustion phase. The amplitudes of subsignals represent pressure oscillation of premixed combustion.

19 4 The wavelet relative energy at fourth layer is the largest. With the increase of DME proportion, wavelet relative energy at fourth layer increases, but wavelet relative energy at other layers decreases.

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