Table of Contents
What is Direct Injection | What is Indirect injection
Direct and Indirect Injection Systems
Direct injection diesel engine
1. Direct injection diesel engines have injectors mounted at the top of the combustion chamber.
2. The injectors are activated using one of two methods – hydraulic pressure from the fuel pump, or an electronic signal from an engine controller.
3. Hydraulic pressure activated injectors can produce harsh engine noise.
4. Fuel consumption is about 15 to 20% lower than indirect injection diesels.
5. The extra noise is generally not a problem for industrial uses of the engine, but for automotive usage, buyers have to decide whether or not the increased fuel efficiency would compensate for the extra noise.
6. Electronic control of the fuel injection transformed the direct injection engine by allowing much greater control over the combustion.
Indirect injection diesel engine
1. An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber, called a pre-chamber or ante-chamber, where combustion begins and then spreads into the main combustion chamber, assisted by turbulence created in the chamber.
2. This system allows for a smoother, quieter running engine, and because combustion is assisted by turbulence, injector pressures can be lower, about 100 bar (10 MPa; 1,500 psi), using a single orifice tapered jet injector.
3. Mechanical injection systems allowed high-speed running suitable for road vehicles (typically up to speeds of around 4,000 rpm).
4. The pre-chamber had the disadvantage of increasing heat loss to the engine’s cooling system, and restricting the combustion burn, which reduced the efficiency by 5-10%. Indirect injection engines are cheaper to build and it is easier to produce smooth, quiet-running vehicles with a simple mechanical system.
5. In road-going vehicles most prefer the greater efficiency and better controlled emission levels of direct injection.
6. Indirect injection diesels can still be found in the many ATV diesel applications.
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