Encyclopedia > Direct injection vs indirect injection
In an indirect injectiondiesel enginefuel is injected into a small prechamber which is connected to the cylinder by a narrow opening. The initial combustion takes place in this prechamber. This has the effect of slowing the rate of combustion, which tends to reduce audible noise.
In a direct injection diesel engine, fuel is injected directly into the cylinder. The piston incorporates a depression (often toroidal) which is where initial combustion takes place. Direct injection diesel engines are generally more efficient than indirect injection engines, but have a tendency to produce greater amounts of audible noise.
In either case the location where combustion takes place, called a swirl chamber, is carefully designed to ensure adequate mixing of the atomized fuel with the compression-heated air.
Directinjectiondiesel engines operate by having the fuel injector arranged to inject fuel directly into the engine's cylinder, as opposed to indirectinjectiondiesel engines, where the fuel is injected into a pre-combustion chamber.
The reduced material volume of the directinjectiondiesel engine reduces heat losses and thereby increases engine efficiency, at the expense of increased combustion noise.
A directinjection engine is also easier to start when cold, due to the reduced heat loss of the design.
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