1. Intake Stroke:
* Gasoline Engines: During the intake stroke, the intake valve opens, creating a significant vacuum in the cylinder. This draws in a mixture of air and fuel, filling the cylinder with a relatively light mixture.
* Diesel Engines: Diesel engines only intake air during the intake stroke. The air is compressed to very high pressures, creating a much denser charge in the cylinder. This dense air is crucial for efficient combustion.
2. Compression Ratio:
* Gasoline Engines: Typically have compression ratios between 8:1 and 12:1.
* Diesel Engines: Have significantly higher compression ratios, ranging from 14:1 to 25:1. This high compression is what ignites the fuel, so there's less reliance on spark plugs.
3. Fuel Injection:
* Gasoline Engines: Fuel is injected before the intake valve opens, contributing to the vacuum created during the intake stroke.
* Diesel Engines: Fuel is injected directly into the cylinder during the compression stroke, after the air has already been compressed. This means the fuel doesn't contribute to the vacuum during the intake stroke.
4. Turbochargers:
* Diesel Engines: Many diesel engines use turbochargers to increase the air pressure entering the cylinders. This further reduces the vacuum created during the intake stroke, as the pressure from the turbocharger overcomes the vacuum created.
Why Does Lower Vacuum Matter?
Lower vacuum in diesel engines can impact some things:
* Engine Braking: The vacuum in the intake manifold helps with engine braking, as it creates resistance against the engine's rotation. Diesel engines have less engine braking due to lower vacuum.
* Fuel Efficiency: The lower vacuum can slightly affect fuel efficiency, though other factors are more influential in diesel engine efficiency.
* Emissions: Some emissions control systems rely on vacuum, so the lower vacuum in diesels can influence their performance.
It's important to note: Lower vacuum in diesel engines is not a disadvantage in all scenarios. It's actually a result of their high compression and direct injection systems, which are designed to maximize power and fuel efficiency. The lower vacuum is simply a consequence of their unique operation.
