Week-4 : Basic Calibration of Single cylinder CI-Engine
1.Compare SI vs CI and list down differences (assignment no 2-SI)
2.Comments on following parameters
- BSFC
- Exhaust Temperature
- A/F ratios
When SI and CI engine are compared, the main difference would be compression ratios. Because of the self-injection, CI engines need more compression ratios when compared to SI engines. When we compare SI and CI engines at same speed i.e., 3600 rpm, The differences in few parameters are as follows:
Engine geometry SI vs CI
It can be clearly see that SI engine has a compression ratio of 9.5 and CI engine has 16.5. Also CI engine is bigger than SI engine in terms of Bore and stroke length.
Engine performance SI vs CI
As it can be seen, the brake power and torque are higher in CI engine. The fuel copnsumption, BSFC, is higher for SI engine when compared to CI engine ( 362 g/kW-h Vs 238 g/kW-h). Higher A/F ratio in CI engine ( 20 Vs 10 ) is contributing to the higher power and torque.
Cylinder predictions:
Here, it can be seen that the exhaust temperatures are higher in the CI engine ( 1039 K Vs 994 K). This can be considered because of the high self ignition temperatures in CI engines. When we see pollutants, it is evident that Nox is higher in CI engine. This can be controlled with the help of EGR, which effects the incylinder temperatures. The CO and HC are higher in SI engines because of poor burning and rich combustion.
3.Change MFB 50 and observe impact on performance
The main duration has been changed to low medium and high ranges as shown below in the case set up.
It can be seen that, with the increase of main duration for burning, the combustion will be slower leaving the engine with low torque requiring more fuel consumption and low temperatures. Also, when we decrease the main duration for burning, it increases brake efficiency, temperature, power and reduces the fuel consumption. It is seen that there is no important effect on A/F ratios with the change of Main duration.
