Small diesel engine vs small petrol engine

Want to customize a small engine for your own project? If yes, you are most likely faced with the question of choosing a diesel or petrol engine. What do you need to know about these two engines? Is this better than that? Should you choose diesel or petrol? You should be aware of some key differences between these two types of motors. In order to make an informed decision, it's important to have a basic understanding of how both engines work.

What Is The Difference Between Diesel And Petrol Engines?

At the most basic level, a modern small engine works with four simple strokes: intake, compression, power and exhaust. The four-engine strokes are the same, whether diesel or petrol-powered, but there is a critical difference in how the strokes are executed.

Engine operation differences

For small petrol engines, the intake stroke usually involves drawing air and fuel into the combustion chamber. At this time, the small diesel engine only takes in air. Next is compression, where both small engine types compress air into a small pocket. Ignition is controlled individually for each fuel type. Small petrol engines use spark plugs to time and initiate the power stroke. This little arc ignites the air-fuel mixture, and the powerful explosion forces the piston down, producing much-desired horsepower.

On the other hand, small diesel engines have only a small pocket of hot air before the power stroke. As the piston nears the top of its compression stroke, the air is compressed hot enough that when injected with diesel, it ignites instantly. Therefore, the ignition timing of a small diesel engine is driven by the fuel injector. Both small engine types function similarly during the exhaust stroke, where valves open and pistons push exhaust gasses out of the cylinders.

Efficiency difference

While small diesel engines continue to struggle with emissions, they have impressive fuel economy figures compared to small petrol engines. In most situations, small diesel engines are far more efficient. This is mainly due to the aforementioned difference in stroke and the autoignition temperature. The autoignition temperature is the temperature at which the air-fuel ratio burns due to heat alone.

In a small petrol engine, it is critical that the auto-ignition temperature is never reached during the compression stroke, as this can cause combustion before the spark plug ignites, potentially damaging the engine. As a result, small petrol engines have a relatively low compression ratio (the amount of air and fuel that is compressed during the compression stroke) because of the increase in temperature caused by compression.

Since small diesel engines don't have fuel in the mixture during the intake stroke, they can compress air more than diesel's autoignition temperature. A higher compression ratio means greater efficiency, so small diesel engines take advantage of this by injecting fuel into the air after compression.

Air-fuel ratio difference

What makes a small diesel engine run according to the amount of fuel injected? One reason is that small diesel engines can operate over a wide range of air-fuel ratios. Small petrol engines typically operate in the range of about 12 to 18 parts air to 1 part fuel by mass. Usually, this ratio is very close to 14.7:1 because, at this ratio, all fuel and oxygen are entirely used up. However, small diesel engines typically run between 18:1 and 70:1 and can run super lean.

Emissions of CO2 and greenhouse gasses

Small Diesel engines emit less carbon dioxide and greenhouse gasses than small petrol engines. This happens because of the specific type of fuel and the internal efficiency of the small diesel engine. More specifically, a small diesel engine uses fuel with a higher compression ratio than petrol and also outperforms a small petrol engine. Most estimates suggest that small diesel engines emit about 10 per cent less than comparable small petrol engines.

Thermal efficiency

Small diesel engines offer higher thermal efficiency than small petrol engines. This also increases their power and torque, making them the perfect solution for heavy loads. This is because diesel fuel is thicker and has a higher energy density.

The thermal efficiency of a small diesel engine directly affects its fuel economy and operating costs. Due to their fuel efficiency, small diesel engines have a variety of applications, from generators to heavy vehicles.

Engine life cycle

From the above discussion, you can conclude that small diesel engines have a longer life expectancy. They are designed to withstand higher compression. They have thicker castings and cylinder walls, while the cylinder liners are replaceable.

Frequently Asked Questions About Small Gasoline Engines vs. Diesel Engines

Which is the more powerful small engine: diesel or petrol?

When deciding which small engine is more powerful, you must look at two numbers: horsepower and torque. With that in mind, the small diesel engine is the more powerful of the two. The small diesel engine will provide the power you need If you want to use in heavy duty applications. Small petrol engines are a close second, but they lose out to small diesel engines when it comes to power as a measure.

Which small engine is better: petrol or diesel?

Both small petrol and diesel engines are internal combustion engines. Both types of small engines use the four-stroke combustion cycle. However, they vary in structure and function. Small petrol engines use spark plugs, while small diesel engines use compression. 

As a rule of thumb, small petrol engines are more affordable, quieter, and require lower service and repair costs. On the other hand, small diesel engines have a longer life cycle and are more fuel efficient.

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BISON hope this in-depth comparison between small diesel and small petrol engines was helpful to you! If you are looking to purchase small engines, please contact our sales staff immediately. You can also click here to learn about all our small engines.