Week-4 : Basic Calibration of Single cylinder CI-Engine

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

Simulation Models:

• CI

• SI

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:

• Pressure

• Temperature 

• Burn rate

• Mass flow rate

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:

• The CI engine is successfully designed at different combustion duration and the same injection period.
• The post-simulation calibration is done to compare the impact on efficiency and other parameters.