Difference Between Diesel Engine and Petrol Engine

Modern cars are powered by diesel and petrol engines, which work on different principles. Diesel engines use compression ignition to save costs and increase torque, while petrol engines use spark plugs for smoother operation and more power at high rpm. Understanding these differences makes it easier to choose the ideal engine for a given requirement.

Ignition process of gasoline engine

Spark plugs are used in gasoline engines to ignite the mixture of fuel and air. The fuel and air are mixed in the carburetor before entering the cylinder. Once the mixture is in, the piston compresses the mixture. The spark plug ignites the mixture at the right time, creating an explosion that pushes the piston down and generates power.

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Ignition process of diesel engine

Diesel engines do not require spark plugs because they run on compression ignition. The only thing compressed in a diesel engine cylinder is air, which causes a significant increase in temperature. Once the air is properly compressed, diesel is pumped directly into the cylinder. Due to the high temperature of the compressed air, the diesel suddenly ignites, creating combustion that pushes the piston downward.

Combustion Process

The combustion process of a diesel engine significantly affects its performance through various factors, including ignition delay, fuel-air mixing, and combustion efficiency. The following are key aspects of how the combustion process affects diesel engine performance:

1. Ignition delay

Ignition delay is the time from the start of fuel injection to auto-ignition. The shorter the ignition delay, the faster combustion starts, which improves engine performance because more complete combustion leads to higher power output and fuel efficiency. On the other hand, too long an ignition delay can result in incomplete combustion, which can lead to increased emissions and reduced performance.

2. Fuel-Air Mixing

Diesel engines use the heat of compression to ignite fuel that is sprayed into high-pressure compressed air. Small droplets of fuel (atomized) combine with the air.

Proper combustion requires an efficient mixture of fuel and air. A poor mixture results in uneven combustion, more waste emissions, and reduced engine performance. By improving atomization and fuel distribution, you can ensure that every drop of gas contributes (electrode).

3. Combustion efficiency

Diesel engines usually use lean air fuel, that is, more air than fuel. This can make the combustion effect and thermal efficiency better than gasoline engines.

This in turn helps towards stoichiometric combustion, thus controlling NOx emissions, while lean burn will result in reduced fuel consumption and reduced NOx emissions, but will produce unburned hydrocarbons (HC) and carbon monoxide (CO). However, it does result in the vehicle producing NOx emissions which need to be controlled via aftertreatment systems.

4. Pressure and Temperature Dynamics

The rapid combustion of the fuel-air mixture creates high pressure inside the cylinder, which is essential for driving the piston and producing power.

The rate at which heat is released during the combustion process affects the thermal efficiency of the engine. Optimizing the heat release rate can improve overall performance and reduce heat losses.

5. Fuel characteristics

The cetane number of diesel affects ignition quality. Fuels with higher cetane numbers result in shorter ignition delays and smoother combustion, which improves performance.

The temperature of the fuel affects its viscosity and density, which in turn affects the injection characteristics and combustion efficiency. The higher the fuel temperature, the better the atomization and combustion performance.

Here is a summary of all the differences between diesel and petrol engines:

scope	Gasoline Engine	diesel engine
ignition	See more : Optical Illusion Brain Challenge: If you have Hawk Eyes Find the Number 70 in 15 Secs Spark plug ignition	Compression ignition (no spark plug)
Combustion type	Homogeneous (fuel is mixed with air before ignition)	Heterogeneous (compress air first, then inject fuel)
Fuel Type	gasoline	diesel engine
Compression ratio	Lower (usually 8:1 to 12:1)	Higher (usually 15:1 to 23:1)
efficiency	Generally low efficiency	Generally high efficiency
Power Output	Higher power output at higher speeds	Higher torque at lower speeds for heavy-duty applications
Fuel Economy	Consumes more fuel for the same power output	See more : Optical Illusion Brain Test: If you have Eagle Eyes find the number 634 among 684 in 8 Seconds? Improves fuel efficiency, especially under heavy loads
Vibration and noise	Smoother operation, less vibration and noise	Higher vibration and noise levels
Maintenance costs	Reduce maintenance costs	Higher maintenance costs, but longer component life
Initial Cost	Typically lower initial cost	Initial costs are usually higher
application	For light vehicles such as cars and motorcycles	For heavy vehicles such as trucks and buses
Environmental impact	CO2 emissions decreased, but CO emissions increased	Emit more carbon dioxide, but less carbon monoxide

The choice of diesel or gasoline engine depends on the intended use. Diesel engines offer superior fuel efficiency and torque for heavy-duty tasks, but have higher maintenance costs. Gasoline engines are suitable for light vehicles, have smoother performance, and accelerate faster, making them ideal for everyday driving.

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Source: https://dinhtienhoang.edu.vn
Category: Optical Illusion