Week-4 : Basic Calibration of Single cylinder CI-Engine
1.Compare SI vs CI and list down differences (assignment no 2-SI)
| SI Model | DI Model |
| Fuel injector is placed on intake port( port injection) | Fuel is directly injected in to the combustion chamber |
| low compression ratio | high compression ratio |
| For the same load and speed produced low torque and power | For the same load and speed produced high torque and power |
| Airflow rate is lower | Airflow rate is higher |
| Emission is higher ( due to low airflow rate) | Emission is less due to lean combustion |
| Lower compression ratio and hence low in cylinder pressure | Higher compression ratio and higher prerssure |
| Higher in cylinder temperature due to higher CV of fuel | Lower incylinder temperature |
2.Comments on following parameters
- BSFC
- Exhaust Temperature
- A/F ratios
Brake-specific fuel consumption (BSFC) is a measure of the fuel efficiency of an engine that burns fuel and produces power. It is typically used for comparing the efficiency of internal combustion engines with a shaft output. It is the rate of fuel consumption divided by the power produced.
From the simulation at a speed of 3600 rpm, it was found CI had better BSFC compared to SI engine. Because the CI engine operate at lean mixture produce better performance parameter due to higher compression ratio while SI engine operates at stoichiometric air-fuel ratio which requires more fuel. hence it shows more BSFC.
Exhaust Temperature: Exhaust temperature varies depending on compression ratio, type of fuel, etc.
even though SI engine works at stoichiometric AFR Exh temperature is more because of higher CV of fuel.
A/F ratios : SI engine runs at stoichiometric AFR (14.5:1) and DI operates at (20.77:1) lean condition. Since CI engine has a higher compression ratio and higher volumetric efficiency it produces better results even at lean mixture.
3.Change MFB 50 and observe the impact on performance
MFB 50% is changed to 0, 5, 8,10, and 12 degrees. observations are as below.
Performance parameters
Emission
In cylinder pressure variation
Exhaust temperature
MFB 50 means, in cylinder the 50% of charge burning angle which we are controlling.
When MFB 50% was varied, there was no significant change in torque and power output
Delaying the MFB leads to incomplete combustion and leads to higher HC and CO emissions.
While calibrating an engine MFB optimization is very important.