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Aim: Basic Calibration of Single cylinder CI-Engine Objective: 1. Compare SI vs CI and list down differences (assignment no 2-SI) 2. Comments on the following parameters BSFC Exhaust Temperature A/F ratios 3. Change MFB 50 and observe the impact on performance Comparison: SI vs CI S.No./Engine type …
Ravi Shankar Yadav
updated on 15 Aug 2022
Aim:
Basic Calibration of Single cylinder CI-Engine
Objective:
1. Compare SI vs CI and list down differences (assignment no 2-SI)
2. Comments on the following parameters
3. Change MFB 50 and observe the impact on performance
Comparison:
SI vs CI
S.No./Engine type |
SI engine |
CI engine |
1. |
It is an engine in which the spark is used to burn fuel. |
It is an engine in which heat of compressed air is used to burn the fuel. |
2. |
SI engine works on Otto cycle |
CI engine works on Diesel Cycle |
3. |
It draws a mixture of fuel and air. |
It draws only air during suction stroke. |
4. |
The carburetor is employed to mix air and petrol. |
The injector is responsible to inject fuel. |
5. |
SI engine has a compression ratio of 6 to 10. |
CI engine has a compression ratio of 15 to 25. |
6. |
These are high-speed engines. |
These are the relatively low-speed engine. |
7. |
SI engines are lighter and cheaper, due to the low compression ratio and maintenance cost is low. |
CI engines are heavier and costlier, due to the high compression ratio and maintenance costs are high. |
8. |
The pressure at the end of compression is 10bar. |
The pressure at the end of compression is 35bar. |
9. |
The thermal efficiency is up to 26%. |
The thermal efficiency is around 40%. |
10. |
The SI engine is generally employed in light-duty vehicles such as scooters, cars, motorcycles, etc. |
The CI engines are generally employed in heavy-duty vehicles like trucks, buses, earth movers, etc. |
Simulation Models:
BSFC - Brake-specific fuel consumption abbreviated BSFC and also known by the term power-specific fuel consumption or simply specific fuel consumption, is a type of comparison ratio that looks at an engine’s fuel efficiency in terms of how much fuel the car uses versus how much power it produces. The formula for calculating brake-specific fuel consumption is fuel consumption divided by power, and often the results are expressed in kilowatts per hour.
Exhaust temperature - In modern internal combustion engines, the knowledge of the exhaust gas temperature is necessary for the management and diagnosis of the exhaust gas after the treatment system, as well as for the protection of components that may be sensitive to thermal overloads.
In the diesel engine, after-treatment components that are often actively managed based on exhaust gas temperature include diesel particulate filters (DPF) and NOx reduction catalysts such as SCR catalysts and NOx adsorber catalysts. In stoichiometric petrol engines, the engine management strategy depends on the temperature of the three-way catalyst (TWC).
A/F ratios - Thermal engines use fuel and oxygen (from the air) to produce energy through combustion. To guarantee the combustion process, certain quantities of fuel and air need to be supplied in the combustion chamber. Complete combustion takes place when all the fuel is burned, in the exhaust gas there will be no quantities of unburned fuel. Air-fuel ratio (A/F) is the ratio between the mass of air and the mass of fuel used by the engine when running.
The ideal (theoretical) air-fuel ratio, for complete combustion, is called the stoichiometric air-fuel ratio. When the air-fuel ratio is higher than the stoichiometric ratio, the air-fuel mixture is called lean. When the air-fuel ratio is lower than the stoichiometric ratio, the air-fuel mixture is called rich. For a gasoline engine, the stoichiometric air-fuel ratio is around 14.7:1 and for a diesel engine, it is 14.5:1.
Mass fraction burned (MFB) in each individual engine cycle is a normalized quantity with a scale of 0 to 1 or in percentage, describing the process of chemical energy release as a function of crank angle.
We will change the parameter called the main duration, which is the duration of crank angle in degrees, where fuel is going to burn by the main diffusion or where controlled combustion is happening. The default value of the main duration is 35, we will change it to 50 means we are increasing the duration of main diffusion combustion. Mainly, a drop in burn rate is expected, because burn duration has increased.
Case setup:
Results:
Engine performance:
BSFC at MFB 50= 238.2 g/kw-hr
A/F ratio at MFB 50=20.78
BP at MFB 50=48.6 kw
From the engine performance, it is seen that with an increase in combustion duration, the BP of the engine decreases and vice versa. The brake efficiency increases with combustion duration but for NOx ppm, it is lower for more combustion duration.
Conclusions:
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