That's not what the first law says. It says that ΔU = Q - W: any change in the internal energy of a system must come from heat entering/leaving the system or work done on/by the system. The convention used here is that positive W is the work done by the system, hence the negative sign.xJJx said:
Thermal efficiency is a measure of how well an engine converts heat energy from fuel into mechanical energy. It is expressed as a percentage and is a key factor in determining the overall efficiency of an engine.
Thermal efficiency is calculated by dividing the work output of an engine by the heat energy input. The heat energy input is the total amount of energy contained in the fuel, while the work output is the amount of energy that is converted into mechanical work by the engine.
The thermal efficiency of a Diesel engine can be affected by several factors, including the compression ratio, air-fuel ratio, fuel type, combustion chamber design, and engine speed. Higher compression ratios and leaner air-fuel mixtures typically result in higher thermal efficiency.
Diesel engines are known for their high thermal efficiency compared to other types of engines, such as gasoline engines. This is because Diesel engines operate at higher compression ratios and use a leaner air-fuel mixture, which allows for more complete combustion and better energy conversion.
The thermal efficiency of a Diesel engine can be improved by optimizing the combustion process, improving the engine design, and using more efficient fuel injection systems. Regular maintenance and proper tuning can also help to maintain high thermal efficiency over time.
