COMPARISON OF SI VS CI AND NOTICE THE EFFECT OF MFB 50
- Compare SI vs CI and list down differences:-
Ans:-
Differences b/w SI engine and CI engine:-
- Parameter
- SI engine
- CI engine
Definition:-
It is an engine in which the spark is used to burn the fuel.
It is an engine in which heat of compressed air used to burn the fuel.
Fuel uesd:-
Petrol is used as a fuel.
Diesel is used as a fuel.
Operating cycle:-
Its operates on Otto cycle.
Its operates on Diesel cycle.
Compression ratio:-
It as a low CR.
It as a high CR.
Thermal Efficiency:-
High Thermal Efficiency.
low Thermal Efficiency.
Method of ignition:-
Spark plug is used to produce the spark for the ignition.
heat of compressed air is used to produce the spark for the ignition.
Engine speed:-
High engine speed.
Low engine speed.
Pressure generated:-
Low Pressure is generated after combustion process.
high Pressure is generated after combustion process.
Canstant parameter during cycle:-
Canstant volume cycle.
Canstant pressure cycle.
Intake:-
Air + Fuel.
only Air.
Weight of engine:-
SI engine has a less Weight.
CI engine has a more Weight.
Noise production:-
It has produce less noise.
It has produce more noise.
Starting:-
Starting of SI engine is easy.
Starting of CI engine is difficult.
Production of hydrocarbons:-
Less hydrocarbon is produced.
More hydrocarbon is produced.
- Comments on following parameters:-
BSFC:-
Ans:- To generate 1Kw of power how much fuel is consumed is called Brake specific fuel consumption.
The BSFC is given by the formula
`BSFC = (BP)/(FC*CV)`
Where,
BP = Brake power in Kw
FC = Total fuel consumption in liters/given time
CV = Calorific value of the fuel
Diesel = 45.5Mj/kg
Petrol = 45.8Mj/kg
Exhaust Temperature:-
Ans:-
Exhaust gas temprature is varies with the type of engine,fuel,ignition quality,compression ratios and other parameters.
Quoting an average.......it is near about 400C
In vehicles with catelytic converters the temprature of the exhaust atleast 250-300 Degre Celsius. Below this temprature, catelytic converters cannot function.
Thermal converters actually works at 600-700Degre Celsius. The presence of catalysts such as platinum, palladium, Cerium oxide, Rhodium allow the conversion of the hermfull emissions of the engine such as NOx,CO,HCs etc to be converted into harmeless molecules such as H2o,N2 and CO2 at amuch lower temprature.
However the exhaust gases themselves may be at a temprature anywhere b/w 400-900Degre Celsius for SI engines and 200-500Degre Celsius for CI engines.
A/F ratios:-
Ans:-
It is defined as the mass of air (ma) to mass of fuel (mf) used by the engine when running.
A/F ratios is given by the formula = `(Ma)/(Mf)`
Where,
Ma = mass of air
Mf = mass of fuel
The inverse ratio called Fuel-to-Air ratio
Fuel-to-Air ratio is given by the formula =`(Mf)/(Ma)`
The ideal A/F ratio, for a complete combustion is called stiochometric A/F ratio. For a gasoline (petrol) engine,stiochometric A/F ratio is 14.7:1. This means that in order to complete 1kg of fuel burn we need 14.7kg of air.
When the A/F ratio is higher than the stiochometric A/F ratio, the air-fuel mixture called lean.When the A/F ratio is lesser than the stiochometric A/F ratio, the air-fuel mixture called rich.
- Change MFB 50 and observe impact on performance:-
Combustion phase variations in diesel engines due to production tolerance, engine, aging, and different combustion conditions cause performance deterioration of fuel economy, torque, and emissions. Therefore, the combustion phase should be controlled by feedback information. A well-known method to control the combustion phase in mass fraction burnt 50% (MFB50) control using in cylinder pressure. MFB50 control can retain performance through combustion conditions. However, MFB50 can compensate only for variations caused by combustion phase changes therefore, further study is required to supplement the limitation of MFB50 control. In this study, to analyze the effect of MFB50 control on combustion, MFB50 is controlled by adjusting the main injection timing using in-cylinder pressure at 1500rpm and a BMEP of four bar according to engine parameter changes. The parameters are fuel rail pressure, boost pressure, mass air flow, swirl valve open, main injection quantity, pilot injection timing, and quantity. While the engine parameters were changing, the influence of MFB50 control on the combustion and emissions was analyzed to establish improvement points for combustion feedback control. Our experiments demonstrated that MFB50 control reduced NOx dispersions but at the cost of increasing PM dispersions. Therefore, to improve MFB50 control, a control algorithm that can handle PM emission dispersion needs to be considered.
We can vary the main duration it will effect directly on our MFB 50 and we observe with the following output.
The following case setup will shows the change in main duration.
Input:-
speed N = 3600 rpm for all three cases
Output:-
We observe the output in the above table
We compare the all above three cases first case is better than the other two as we increase the main duration it will reduce the power output and also reduce the brake torque and increases in the BSFC for the remaining same condition as we see in the above results.
We increase in the main duration the inside cylinder pressure in decreases accordingly.