SI Engine vs CI Engine Calibration using GT Power


       The objective of the project is to compare the SI vs CI Engine parameters for the BSFC, Exhaust temperature and A/F ratio. Change the MFB 50 and observe the impact on performance.


        The GT Power has various tutorial files that are used to find the results depending on our requirements.

        The single-cylinder CI Engine was used for this project and save the file.

Tutorials --> Engine performance --> 01-1 cylDIorSI --> 1 cylDI-final.gtm.

       The emission parameter of the engine NOx is added for the simulation using cylinder Cylinder --> COmbustion object --> Comb --> Advanced --> NOx.


Then the plot which is required for the results is selected under the cylinder block.

       Flow - Pressure, Pumping loss, P-V Diagram, Volume, Value mass flow & lifts.                       Thermal - Temperature, heat transfer rate.                                                                         Combustion - Burn rate, In-cylinder energy balance.                                                           Composition - NOx concentration.

    Select the F4 option to open the case set up to add more cases use option Cases --> Append cases.


Select run option to run the simulation and unselect the run each case in parallel option and select the show the graphical user interface under simulation option and confirm it by clicking the finish option and simulation starts to run.

The link for SI Engine project is attached below:


The brake power, torque and all the engine performance have been improved when compared to the CI engine this is mainly due to the increase in the compression ratio. 

i) BSFC - The fuel consumption has been reduced even though the engine performance has all increase so this will eventually increase the efficiency of the engine. 

                          efficiency (%) = Output energy/ Input energy.

The Input energy is the mass of fuel * Calorific value.    

The calorific value of diesel fuel is roughly 45.5 MJ/kg, slightly lower than petrol which is 45.8 MJ/kg. However, diesel fuel is denser than petrol and contains about 15% more energy by volume. The density of diesel is about 0.832 kg/L & has a density of petroleum about 0.745 kg/L.

ii) Exhaust Temperature - The exhaust temperature of the CI Engine & SI Engine 

a) CI Engine


b) SI Engine


The exhaust temperature and max temperature of the CI engine are less than the SI engine the diesel burn on self-ignition whereas the petrol an external source of heat is produced so the max & exhaust temperature is high. The inlet conditions of both the engine are the same.

A/F Ratio 

The A/F ratio is always higher in diesel engine, the diesel can burn on a wide range of A/F ratio whereas the petrol and air get mixed well before the injection and so it has less value on A/F ratio. 

MFB Parameter

Main Duration: Duration in crank-angle degrees of the main diffusion burn or the name of a dependency reference object. The duration should exclude the first 10% and the last 10% of the area under the main burn curve.

Case setup:

Engine Performance:

On increasing the main duration value the brake power, torque, efficiency decreases but the fuel consumption increases so this actually affects the output of the engine. 

The Max temperature & NOx value decreases by increasing the duration time which is the advantage of increasing it but the emission can be reduced by using different devices so increasing the duration time to 50 has really no effect.


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The End