Single Cylinder SI Engine Modeling(1D)

AIM

1. Run the case at 1800 rpm and list down important parameters.

• airflow rate
• BMEP
• BSFC
• In-cylinder pressure

2. Increase the power output at 3600 rpm by 10%.

INTRODUCTION

A spark-ignition engine (SI engine) is an internal combustion engine generally petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to the compression-ignition engine, typically diesel engine, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.

MODELING OF SI ENGINE(Single Cylinder)

The SI engine modeling has been done by importing various Components from the template library to the project library. Various templates that are imported are :

Components

• EndEnvironment: This template is used to describe the boundary Conditions for inlet and outlet.
• PipeRound: This template used to model around the cross-section pipe.
• EngCylinder: This template used to describe the attributes of engine cylinders which is used to describe the heat transfer model and wall temperature.
• EngineCrankTrain: This object is used to model the Cylinder geometry and also the Kinematics of the engine.

Connections :

• OrificConn: This template models an orifice, defined by diameter or area and discharge coefficients, which calculates the mass flow rate between the adjacent flow volumes. 'OrificeConn' parts represent the plane connecting two flow components.
• ValveCamConn: This template defines the characteristics of a cam-driven valve including its geometry, lift profile, and flow characteristics.
• InAFSeqConn: This template is used for the operation of a sequential pulse fuel injector, most commonly in SI engines. The user imposes the fuel-to-air ratio, and the resultant injection pulse width is calculated for each injection event.

After importing the various templates the flow tree should look like this :

BASE CASE SETUP

Inlet Environment

To create the inlet boundary condition, double-click on the 'EndEnvironment' template to create a new object, and name the object as env-inlet.

Pressure and temperature boundary conditions are provided and for composition, GT-ISE expects a reference object that describes the fluid composition of the inlet ambient environment. We have selected 'air' under FluidMixture which has predefine mixture nitrogen and oxygen.

Intake Runner

The intake runner will connect to the intake port, this can we create with the pipe round template. Name the object 'intrunner'. For the Surface Finish, the “Roughness from Material” is selected with a smooth_plastic option for the SI engine. This does not mean that the part is made of plastic, but that the surface roughness of the part is that of typical smooth plastic.

For the 'Initial State Name' attribute from 'Template Library' select 'FluidInitialState' and provide value for temperature. pressure. For the 'Composition' we have selected the FluidMixture 'air'.

Intake Port

Next, we will create an intake port of the engine, this will be created with the 'pipeRound' template, and rename it to be Intake_port. The Imposed Wall Temperature is set to 450 K and the Heat Transfer Multiplier is set to 1.5 to represent heat transfer from the hot valve.

Intake and Exhaust Valves

It is now time to define the camshaft and valve characteristics of the engine. We are going to copy the valve connection for the intake and exhaust valve which is provided in the template.gtm file. Here, we provide the cam timing and lift profile.

Intake_Valve

Exhaust_Valve

Cylinder

Double-click on the 'EngCylinder' template located in the project library of our file and Name the object "cylinder".It defines sub-models for the cylinder such as geometry, wall temperature, heat transfer, in-cylinder flow, and combustion, most of these valves are selected with reference.

Exhaust Port and Runner

Exhaust port and runner are created by copying and pasting the inlet port and runner and renaming the port for exhaust. For the exhaust side, the 'Initial State Name' attribute selected from the 'Template Library' is 'FluidInitialState' and their value has been modified. And For the composition, we have chosen 'FluidMixtureBurned'.

This object is used to make mixtures of burned fluids where the specified species will be replaced by the products of combustion produced by burning the specified species.

Outlet Environment

To create the exhaust EndEnvironment the inlet EndEnvironment object "env-inlet" will be copied and edited. We have also change the Reverse Flow Composition to "track". This is the recommended flag for the exhaust EndEnvironment. This flag indicates that when there is reverse flow from the exhaust environment back into the exhaust pipe, that the temperature of the gas entering from the environment will be equal to the exhaust gas temperature from the last timestep, rather than the ambient temperature.

Engine Crank Train

The final object to create for this model is the engine crank train. This object defines the engine type, cylinder arrangement, firing order, and other engine block and crankshaft characteristics. We are using 'Engine Speed' as a parameter. For engine friction, we are using the Chen-Flynn model, which is a common engine friction model. This friction includes and accounts for all friction from the crank train, pistons, and valvetrain.

It is now time to place parts on the project map and connect the components together. A part is created when an object is dragged and dropped onto the project map (same as a copy and paste operation). Click and hold on every required object and drag it on the map.

Each object that is seen on the map is now an individual part. Now it's time to connect part together. This is done by selecting a link option from the Home menu and selection parts in order to connect together. Continue connecting the parts together from left to right in the general flow direction. After the main flow path has been connected, connected the injector to "intport" for SI and the cylinder to the "Engine".

SI Injector Model

The next object that will be defined is the fuel injector. For the "Fluid Object" attribute in the Timing-General, we have selected "indolene-combust".The injector will need a Part Name for the Air Mass Flow Rate Sensor. Now that the parts are connected, one can easily define the air mass flow rate sensor for the SI injector.

To specify the moving average mass flow rate sensor, first, select the radio button next to "Part Name” for “Air Mass Flow Rate Sensor". We would like to select the orifice upstream of intrunner-1, which is OrificeConn part 1. That's why we have selected "1" which will be filled into the attribute in the injector.

In the 'Timing-General' folder, the “Part on Map” has to be specified under “Source of Angle”., which we have selected as 'cylinder_1'.

The below image shows the complete map of the SI engine model.

RUN SETUP
The next step is to define the run setup. We have to define the following values TimeControl, Initialization, and FlowControl. In FlowControl, for the “Time Step and Solution Control Object” use the Value Selector and choose the Explicit option under FlowControlExplicit. We have also define maximum stimulation duration to be 10 cycles.

Plot Setup
Plot Setup, which is found under the Model setup pull-down menu, gives the user a variety of options to change the way in which the plots are plotted. Cycle and/or time plots may be output by selecting the appropriate plot from the "Plot Options" folder within each part. Each of these plots will be stored. The below figure shows the plots which we have selected for various components:

For base setup, we ran the 1D simulation with RPM of 1800, which we have selected as a parameter to define.

RESULT

DATA SUMMARY

• Air-Flow Rate: Airflow rate is used to describe the amount of air entering into the cylinder for combustion. It is calculated in our case to be 23.9 kg/hr
• BSFC(Brake Specific Fuel Consumption): It is a measure of the fuel efficiency of any prime mover that burns fuel and produces rotational or shaft power. It is typically used for comparing the efficiency of the internal combustion engine with a shaft output.
• BMEP(Brake Mean Effective Pressure): It is the average pressure which, if imposed uniformly on the pistons, would produce the measured power output (brake). The key is that BMEP is a theoretical value, not a measured value.

BMEP = IMEP - FMEP

BMEP = 10.23 - 1.13

= 9.1 bar

• In-Cylinder Pressure: In-cylinder pressure is used to describe the pressure developed inside the cylinder during combustion. It is calculated as 49.5 bar.

PLOTS

P-V Diagram

The given graph shows the actual SI engine cycle, it shows all process of SI engine, that is suction at beginning then compression, power stroke, and exhaust stroke.

Cylinder Pressure

The given graph shows the maximum pressure attained in the combustion chamber, during the compression stroke. The cylinder pressure here is 49.5 bar.

Valve Lift

The given graph shows the intake valve and exhaust valve opening timing. We can see that there is an overlap between the intake and exhaust valve opening, which can be improved by optimization of valve timing.

PART -2

Increase the power output at 3600 rpm by 10%.

Power output can be increased by these factors :

• Compression Ratio:

Increasing the compression can increase the power output of the engine but in the case of the SI engine, too much Compression ratio can cause the knocking effect in the engine which will damage the engine.

• Fuel Ratio :

Making the mixture leaner by decreasing the air-fuel ratio, makes increases the fuel consumption in the engine.

• Geometry :

Changing in the geometry of the crank train geometry so that stroke to bore ratio changes, i.e., change in bore and stroke can cause an increase in the power output.

Condition --1

We will be analyzing the change in bore diameter effect on the power output of a single-cylinder SI engine.

The below table shows the change in power output by increasing the bore diameter.

We can see that, by changing the bore diameter just by 4mm increase the power by 10% from actual power output.

Condition --2

In this, we have analyzed the effect of change in the compression ratio on SI engine power output.

The below table shows the change in a compression ratio and its effects.

From the given output we can see that changing the compression ratio from 9.5 to 14.5 increases the power output by 10% but this can cause a knocking effect in the SI engine which can damage the engine.

Condition --3

In this analysis, we are changing the inlet pressure in the scientific method, we can say to know the effect of turbocharging. Below table shows the details for the change of initial pressure :

From the given table we can see that by turbocharging, just a small increment in increasing the inlet pressure increase the power output by 10%.

Conclusion

• 1D modeling of the SI engine has been successfully performed.
• We can also that increasing the bore diameter, stroke, compression ratio, or turbocharging increases the power output of the SI engine.