Changing Fuel Properties in a Compression Ignition Engine

Hi, i'm currently replicating an experiment to simluation for a Compression Ignition Engine. My purpose is to analyse the BSFC, power, BTE, and emission comparison between a diesel fuel and alternative biodiesels.

I tried using 2 models, one is using Mapped CI engine with my own setup, and the other one is from th example model of CI engine dyanamometer. There's 2 issues that i'm facing right now.

1. I need to make the model to be able to change fuel properties freely. previous version of Fuel block are able to do that, but the 2025 Fuel block version couldn't be used as it will assumes all fuel are at isothermal condition, which is not ideal for a replication from experimental data.

As for the existing CI engine blocks and models available, they use a fixed set of data for diesel fuel. the MApped CI engine can be altered, however i do not have the MApped data of the fuels that I am using.

The fuel properties that i want to change is by altering the fuel's density, kinemetic viscosity, calorific value, cetane number, and if possible, oxygen content.

2. Both models are giving me the 3 outputs that i needed, but only by values, without any grapgh. Maybe i just need to make a connection to scope.

I would really appreatiate if there's any help on this. Thank you

Answer 1

[Adarsh]

Hi @Adlina,

Based on my understanding, you're simulating a CI engine to compare diesel and biodiesel fuels for BSFC, power, BTE, and emissions analysis. You need to modify fuel properties and add graphical outputs.

For fuel property modifications you can use the CI Core Engine block.

Parameters you can change directly (exact values) in the CI Core Engine Block:

1. Calorific value - "fuel_lhv" parameter (J/kg)
2. Density - "fuel_sg" parameter (specific gravity, dimensionless)
3. Oxygen content - "afr_stoich" parameter (stoichiometric air-fuel ratio)

Parameters you can estimate:

Cetane number - Approximate through the "f_tqs_mainsoi_eff" efficiency multiplier table. Higher cetane improves combustion efficiency by roughly 0.5% per cetane point.

Parameters that cannot be changed:

Kinematic viscosity - Not available in the CI Core Engine block. This has minimal impact on BSFC and emissions comparisons at this modeling level.

The CI Core Engine block is recommended over Mapped CI Engine when you lack complete dynamometer data for your biodiesel fuels.

To view outputs graphically, connect Scope blocks from the Simulink Library to your output signals (BSFC, power, BTE, emissions) to visualize the results. If the signals you are monitoring are phyical signals in any case you can use the "PS-Simulink Converter" block to convert the physical signal to simulink signal.

For more information on the CI Core Engine block the following documenation link can be referred:

https://www.mathworks.com/help/autoblks/ref/cicoreengine.html

I hope this helps!