Diesel combustion and gas laws

[Denis46]

Hi all, new guy here. I am trying to understand the laws that govern a diesel motor. I know it compresses air at about 17 to 1 to ignite the fuel and I think that fuel will expand the air in the chamber at about 5 times the volume consistently (from tdc to end of stroke). I am trying to figure how many BTUs is used to heat the combustion stroke. Also, is the volume of liquid diesel added to the air important to the volume of the chamber (apart from igniting and expanding the air). I have tried to understand this with V1*P1/T1=V2*P2/T2, including using Kelvin and Pa, but could not make the numbers work.

I hope I have phrased this properly.

This is the first of a few questions to come

Thanks in advance
Denis D.

 

[Dale]

Hi Denis,

Welcome to PF. The amount of BTU's released would be equal to the specific heat of combustion of the diesel fuel times the amount of fuel, but I don't know what either of those two numbers are.

 

[charng]

Hello Denis,

First of all, welcome to the scientific community! It's great to see someone taking an interest in understanding the laws behind diesel combustion.

To address your first question, the amount of BTUs (British Thermal Units) used to heat the combustion stroke in a diesel engine can vary depending on several factors such as the fuel-to-air ratio, engine speed, and load. However, on average, a diesel engine converts about 30% of the fuel's energy into mechanical work, while the remaining 70% is lost as heat. This means that the amount of BTUs used for the combustion stroke would be around 30% of the total energy released by the fuel.

Regarding your second question, the volume of liquid diesel added to the air does not significantly affect the volume of the chamber in a diesel engine. This is because diesel fuel is injected into the air just before combustion, and the volume of the fuel is relatively small compared to the volume of the air in the chamber. Therefore, the volume of the chamber is primarily determined by the amount of air compressed during the compression stroke.

Now, let's talk about the gas laws you mentioned. The equation you referred to, V1*P1/T1=V2*P2/T2, is known as the Ideal Gas Law, which describes the relationship between the pressure, volume, and temperature of a gas. However, in the case of a diesel engine, the air-fuel mixture is not an ideal gas due to the presence of liquid fuel and the high compression ratios involved. Therefore, the ideal gas law may not accurately predict the behavior of the mixture in the chamber.

In conclusion, understanding the laws governing diesel combustion can be complex and may require more advanced equations and models. I would recommend consulting with experts in this field or conducting further research to gain a deeper understanding. I hope this helps, and I wish you all the best in your scientific journey!