Experimental investigation on influence of EGR on combustion performance in SI Engine

M. Božić, A. Vučetić, D. Kozarac, Z. Lulić

INTRODUCTION

EXPERIMENTAL TESTING

RESULTS

Corresponding author:Mladen Božić, mag.ing.mechUniversity of ZagrebFaculty of Mechanical Engineering and Naval ArchitectureIvana Lučića 5, 10002 Zagreb, CroatiaE-mail: mladen.bozic@fsb.hr

Figure 1. Experimental IC SI Engine testbed

Table 1. Engine specifications

In this research, the use of stoichiometric air-fuel mixture withexhaust gas recirculation (EGR) technique in spark-ignition enginewas experimentally investigated and its influence on main SIcombustion parameters is shown. Experimental setup on which thisresearch is performed consists of SI engine, AC Dyno, software forcontrol of engine and dyno, and various measurement devicesincluding the indicating equipment for SI engine. The research isperformed by comparing the SI operation at specific load with andwithout EGR.

In order to achieve optimal results from the combustion with EGRdilution spark timing was optimized. Optimized spark timingmeasurement points are selected from the acquired values of IMEPand MAPO (maximum amplitude pressure oscillation) shown on thenext two figures. The optimized conditions for the selectedmeasurement points were highest achieved IMEP without theoccurrence of knock.

Experimental data was taken for four different cases of EGR dilutionat constant speed of 1600 rpm. All four cases were optimized bymultiple measurement points with spark sweep performed from verylate towards early ignition up to the point where knock combustionoccurs. Initial measurements were made with no EGR with sparktiming ranging from -6 to -19 °CA after top dead centre (ATDC). Thesecond case was measurement with 11% EGR with spark timingranging from -16 to -40 °CA ATDC. The third case wasmeasurement with 15% EGR with spark timing ranging from -24 to -50 °CA ATDC and the fourth case was measurement with 20% EGRwith spark timing ranging from -36 to -50 °CA ATDC. The fourth(last) case was not measured up to the point of occurrence of knockbecause cycle to cycle variations were too high resulting in unstablecombustion.

Figure 2. Spark timing and Pressure at IVCof four measured cases

In the presented results two comparisons are made: one with fixedspark timings and one with optimized spark timings.

By looking at the obtained IMEP on the figure above, values of thepoints with significantly different IMEP are chosen to present theinfluence of EGR dilution on combustion. The application of EGRresults in reduced IMEP because the combustion temperature isreduced which results in longer combustion duration, lower peakpressures and lower peak of rate of heat release.

Figure 6. Maximum Amplitude of Pressure Oscillations for optimum spark timing measurement points

Figure 7. IMEP for optimized spark timing measurement points

Figure 8. Coefficient of Variation of IMEP for optimized spark timing measurement points

Figure 9. Nitrous oxides emission for optimized spark timing measurement points

IMEP shows almost linear rise with the addition of EGR dilution upto the limit of combustion stability. The results showed that thecontribution of the diluent effect on IMEP rise was 4.4%, 5.8% and-11.2% for the dilutions of 11%, 15% and 20% respectively.

When dilution of 20% was applied IMEP fell to 5.52 becauseCoVIMEP increased significantly. Therefore with the dilution of 20%the limit on combustion stability was reached as shown of figureabove.NOX emissions show significantly lower values with the applicationof EGR dilution. Even though spark timing was optimized andcombustion was advanced to knock limit, NOX emission decreased.

Increase of cylinder pressure with the input of EGR is influenced bythe higher intake pressure and by advancement in spark timing.Heat release shows longer combustion duration and lower peakrate of heat release with the application of EGR dilution as shownon figure below.

Figure 3. Indicated Mean Effective Pressure for fixed spark timing measurement points

Figure 10. In-Cylinder pressure and Rate of Heat Release for optimized measurement points

Manufacturer Hatz, 1D81

Engine type 1 cylinder 4 stroke

Bore, mm 100

Stroke, mm 85

Combustion chamber Toroidal

Displacement, cm3 667,59

Compression ratio 12

Intake Valve Timing Open @ 340°, Close @ 590°

Exhaust Valve Timing Open @ 154°, Close @ 380°

In this research, the use of EGR strategy was

experimentally investigated in spark-ignition engine. Engine

performance and emissions were studied and following conclusions

have been obtained:

• With the application of EGR dilution significant increase in

CoVIMEP is observed which implies that there is a limit on how

much dilution can be applied in order to cool down the

combustion.

• With the use of EGR abnormal combustion was effectively

suppressed and the engine performance was improved.

• Spark timing and intake pressure optimization is required in order

to achieve higher efficiency when diluting intake mixture with

EGR. In general intake pressure has to be increased and spark

timing advanced.

• Application of EGR dilution significantly reduces NOX emission.

Figure 5. Indicated Mean Effective Pressure for optimum spark timing measurement points

Optimized work points

CONCLUSIONS

Figure 4 . Indicated Mean Effective Pressure for fixed spark timing measurement points