View into a Simscapeblock

Hi all,

I have a question about Simscape blocks. In particular, I am interested in the block “Spark Ignition Engine”.

It performs various calculations related to the operation of a four-stroke engine with external ignition.

I would like to know what formulas are behind the block's calculations so that I can better interpret the results.

The “Description” submenu allows you to access the block's source code.

However, this code only shows what you see in Simulink's graphical interface.

Is there a way to access the mathematical formulas that the block uses to perform its calculations?

The following command takes you to the example project in question:

openExample('sdl/SingleCylinderSparkIgnitionEngineExample')

I would be very happy to receive a reply.

Kind regards,

Florian

Answer 1

[Shivam Gothi]

Hello @Florian Bendel,

As per my understanding, you are trying to understand the mathematical model of "Spark Ignition Engine", but the mathematical equatons describing its dynamics are not stated in the documentation.

"Spark Ignition Engine" block is a composite block that uses a subcomponent implementation of these blocks:

• The SI Combustion Cylinder
• The Ignition Trigger block
• Crankshaft
• Air Intake Block
• Exhaust mainfold thermal

Each of the above documentation explains the mathematical equations that are used to model the perticular sub component.

I analysed the equations of each sub-blocks, and summarising them for your reference.

"SI Combustion Cylinder" block calculates the instantaneous cylinder volume as a function of the crank position. It then finds the time derivative of V(θ), which scales the instantaneous power that the cylinder generates. This documentation explains the valve timing digram.

"Crankshaft" block computes the torque, based upon the crank position "θ".

"Ignition trigger" block takes the spark angle as input at port SA and generates an asynchronous event trigger output at port Trig when the crank position crosses the spark angle

The "Air Intake" block represents an abstract air intake system that computes lumped-parameter air flow dynamics.

The documentation above outlines the mathematical equations that dictate the behavior of a specific sub-component. By connecting these insights, you can derive the comprehensive mathematical framework that governs the entire "Spark Ignition Engine."

I hope you find the information usefull !

[Florian]

Hello @Shivam Gothi,

thank you for your help and feedback.

Yes, I mean the block "Spark Ignition Engine". I also found the other blocks you mentioned for the sub-functions. But I wasn't sure whether the combined block “Spark Ignition Engine” is really based on these. You were able to clarify that, thank you.

In the source code of the block “The SI Combustion Cylinder” there are repeated references to a literature [EN14]. The formulas seem to be discussed in this literature.

How can I find it?

Kind regards

Florian

[Shivam Gothi]

Hello @Florian Bendel,

Can you please tell where is the reference to literature [EN14] mentioned in the documentation? I searched the documentation, but I was unable to find it.

[Florian]

Hello @Shivam Gothi,

Yes, sure. The reference can be found in the source code of the “The SI Combustion Cylinder” component.

I will give you an example in which reference is made to the literature:

You can find this in line 460 and 461:

    % Ideal Otto cycle pressures.  See Figure 5.5 in [EN14] for where the '2'
    % and '3' are in the cycle.

or this, which can be found in line 479 and 480:

    V_23 = EngineCombustionCylinderVolume(cpos, V_c, Rcrk, conrod, bore);
    dTcomb = q_LHV * min(1, afr_ivc/AFR_s) / ((afr_ivc + 1)*Cv_c);  % EN14-(7.44)

I hope you can find this in the source code.

Kind regards

Florian

[Florian]

Can anyone tell me where this source can be found?

Kind regards

Florian Bendel