Week 2 : Basic Calibration of Single cylinder SI-Engine
Assignment 2: Basic SI engine Calibration
Aim:
To perform and solve problems related to basic SI Engine calibration using singe cylinder SI engine model from GT-Suite
Introduction:
In this particular assignment, we would be studying solving problems related to basic SI engine calibration using GT-Suite. For this particular assignment, we would be referring to the single cylinder SI engine model. Refer Fig_1 for the same.
We will first discuss the model. As can be observed from the figure, this model is a very simple model focussing on the engine performance aspect of the SI engine only. Due to this, majority of the other systems like cooling, etc. have been conveniently left out of the equation.
In this particular model the components like inlet/ exhaust runner, port, valve and the engine cylinder have been modelled using available objects. Appropriate boundary conditions also have been assigned to this model in the form of environment objects. Thus, in detail, the particular objects have been used:
- env-inlet/outlet: Done by BoundaryPressure template to fix end conditions
- int/exhrunner: Modelled using PipeRound template to take into account the runner and pipe effects on the airflow.
- int/exhport: PipeRound template is used to take into account the fuel injection that takes place in this Port Fuelled system.
- cylinder & engine: Modelled using the EngCylinder and EngineCrankTrain templates.
- si-inject: Plays the role of the fuel injector and has been modelled using the InjAFSeqConn template.
It is very important to focus on the last object as this defines the fuel delivery method to the engine. As we have mentioned before, the location of this injector signifies that the Port Fuel Injection system has been used, wherein fuel is injected into the inlet port itself to vaporize and form a homogenous fuel-air mixture before entering the cylinder.
After this introduction, we will now move on to the problems mentioned.
Question 1:
Given:
- Engine_speed = 1800 rpm
Find:
- Air Flow Rate
- BMEP
- BSFC
- In-cylinder pressure
Solution:
Keeping all other parameters set constant, we will alter the speed in the Case Steup. Refer Fig_2 for the same
After the simulation, we can find the required values.
For Air flow rate:
Inlet air flow rate: 0.063 kg/s (Refer Fig_3)
For BMEP:
bmep: 11.12 bar………………..(Refer Fig_4)
For BSFC:
Bsfc = 241 g/kW-h (Refer Fig_5)
For In-cylinder pressure:
Max in-cylinder pressure = 48.9 bar (Refer Fig_6)
Thus the required quantities have been found
Question 2:
Given:
Engine speed = 3600 rpm
To-Do:
Increase power output by 10%
Solution:
In order to realize a 10% increase in power, it is essential to find out the initial power output before any modifications. Keeping the default conditions as the same, we simulate the model and find out the power output.
From the model simulation at base conditions, the max brake power has been found out to be 16.69 kW with a pressure rise rate of 2.14 bar/deg (Refer to Fig_7, Fig_8)
A 10% increase would mean that we have to achieve a value of 18.35 kW.
For the above requirement to be satisfied, intake pressure was boosted from 1 bar to 1.1 bar (refer Fig_9), which resulted in the power to be 18.89 kW (refer Fig_10), which is a 13% increase. This was obtained for a minute rise in the pressure rise rate, which came out to be 2.383 bar/deg thus avoiding the problem of knock (Refer to Fig_11).
Thus, the problem has been solved.