ATPL Aircraft General Knowledge - Class 4: Diesel Engines.

Summary

In this video, Grant explores the differences between diesel and petrol engines, focusing on how diesel engines use compression ignition for power generation. Diesel engines are more fuel-efficient due to higher pressure and temperature during combustion, producing more power with less fuel. The video explains the components, such as fuel injectors and glow plugs, and compares the robustness of diesel engines to petrol engines. Although more fuel-efficient, diesel engines are heavier and require better cooling. Environmental and health concerns are also discussed, highlighting the rare use of diesel engines in light aircraft.

Takeaways

• 😀 Diesel engines operate through compression ignition, where the fuel ignites due to the heat generated by compressed air, unlike petrol engines that use spark plugs.
• 😀 In the intake (Suck) phase of a diesel engine, only air is drawn in, as diesel engines use direct fuel injection systems to avoid early ignition due to high compression.
• 😀 The compression (Squeeze) phase compresses the air, raising its temperature and pressure before fuel is injected to create ignition.
• 😀 Diesel engines rely on the compression of air to reach ignition temperatures, which can be supported by glow plugs in cold conditions to preheat the air.
• 😀 Diesel engines are more fuel-efficient than petrol engines due to higher pressure and temperature, generating more power for the same amount of fuel.
• 😀 Diesel engines produce more power for the same size cylinder, with significantly larger pressure and temperature rises during combustion compared to petrol engines.
• 😀 Diesel engines use heavier, more robust components, which increases durability and reduces maintenance needs but also contributes to their overall weight.
• 😀 Diesel engines do not require components like carburetors, spark plugs, magnetos, or distributors, reducing maintenance complexity.
• 😀 Despite their benefits, diesel engines require better cooling systems due to the higher temperatures generated during combustion.
• 😀 Diesel engine emissions pose environmental and health risks, which is why they are less common in light aircraft, where petrol engines are preferred.

Q & A

What is the main difference between a diesel engine and a petrol engine?

The main difference is in how the fuel is ignited. Diesel engines use compression to ignite the fuel, while petrol engines use spark plugs to ignite the fuel mixture.

Why can't you use petrol in a diesel engine or diesel in a petrol engine?

Diesel engines rely on compression to ignite the fuel, and if petrol is used, it could ignite prematurely, damaging the engine. Similarly, diesel doesn't ignite easily with a spark plug, leading to inefficiency or potential damage in a petrol engine.

How does a diesel engine work to ignite fuel?

In a diesel engine, only air is drawn into the cylinder during the induction phase. Then, the air is compressed to high pressures and temperatures. Fuel is injected into the hot, compressed air, causing it to ignite.

What is the function of a glow plug in a diesel engine?

A glow plug adds heat to the cylinder, helping to preheat the air, which improves the ignition of fuel during cold starts. It doesn't create a spark but provides a gentle source of heat.

Why do diesel engines generate more power for the same amount of fuel compared to petrol engines?

Diesel engines achieve higher power due to the higher compression of the air, which leads to greater temperature and pressure rises. This results in more energy being released for the same amount of fuel.

What are the advantages of a diesel engine?

Diesel engines are more fuel-efficient and produce more power for the same amount of fuel. They also require less maintenance because they don't have components like carburetors or spark plugs, and their design is generally more robust.

What is the disadvantage of the heavy components in a diesel engine?

The heavy components of a diesel engine require more power to lift, making it less ideal for use in aircraft, as it reduces the overall efficiency when lifting the engine and the aircraft itself.

How do diesel engines manage the high temperatures and pressures during combustion?

Diesel engines need additional cooling, typically through air cooling or liquid coolant, to dissipate the excess heat generated during the high-pressure combustion process.

What are the environmental concerns with diesel engines?

Diesel engine emissions are harmful to both human health and the environment. They typically produce more pollutants compared to petrol engines, contributing to air quality issues and health risks.

Why are diesel engines less commonly used in light aircraft?

Diesel engines are less common in light aircraft due to their weight and the environmental concerns associated with their emissions. Lighter petrol engines using Avgas are more widely used in these aircraft.