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

Assignment 4: Basic CI engine Calibration

Aim:

To perform basic CI engine calibration

Introduction:

For this particular assignment, we have been asked to explore the single cylinder DI engine model form the GT suite tutorials and study some changes in it. We will explore the model first.

The model as can be seen in Fig_1 represents the inlet to exhaust components of a single cylinder CI engine. The components have been modelled as follows:

• env-inlet/outlet-1: The intake and exhaust terminal connections of the engine modelled using BoundaryPressure template. An interesting point to note here is that the inlet and outlet pressure is set to be 2.4bar thus indicating the presence of a boosting mechanism. Use of the same value at exhaust though was not required.
• int/exhrunner-1: Modelled using the PipeRound object to represent the runners
• int/exhport-1: Again, the PipeRound object is used to model the ports.
• cylinder-1/ Engine: EngCylinder is used to model a single engine cylinder while the EngineCrankTrain object is used to model the rest of the engine.
• di-inject-1: The injector is modelled using the InjDieselSimpleConn template for representing the direct fuel injection in the cylinder.

We will now head on to the questions.

Question 1:

The differences are listed below:

Parameter	SI	CI
Compression ratio	Low (<12)	High (>12)
Application	Light- medium duty vehicles	Heavy and commercial vehicles
Engine pickup	Quick, highly responsive	Contains lag
Fuel efficiency	Low	High
HC, CO emissions	High emissions	Low
NOx	Relatively low	High
Soot emissions	Very low	Hgh
Bossing capability	To be done with care	Standard practice
Overall engine size	Small	Large
Method of ignition	Spark plug	Fuel injection
Throttling losses	High	Very low
In-cylinder air motion requirement	Tumble	Swirl

These were some of the many differences in between the technologies.

Question 2:

The comments are as given below:

• BSFC: bsfc is basically the amount of fuel consumed per unit power generated. Now in a CI engine, the air- fuel mixtures are generally very lean. Due to this a low amount of fuel s always consumed.

Alongside this, the fuel conversion efficiencies of a CI engine are very high, due to which with a very low bsfc, the engine can develop the required power output.

• Exhaust temperatures: This is a very subjective term, as the exhaust temperatures will very with the speed and load. The exhaust temperature will increase with increasing load as well as speed. Also, the use of EGR will again introduce a variation.
• A/F ratios: Diesel engine always runs lean. This is to ensure a high level of fuel conversion efficiency and also to produce the most amount of power.

Question 3:

We will now play around with the values of MFB-50 and observe its effect on power. By default, the MFB 50 value is shown to be 35 CAD as can be seen in Fig_2. Its effect on the brake power is shown in Fig_3. A power output of 36.32kW can be seen.

Now we will decrease the duration to 20 CAD and see the effect. As can be seen in Fig_4 the power output has increase to 39kW due to decreased burning duration of the entire fuel.

Now we will increase the duration to 45CAD. As expected, due to the increased burn duration, the power output obtained is only 33kW (refer Fig_5).

So a +- 15CAD difference on both sides lead to a -+ 3kW power output difference

Thus all the questions have been solved.