Turbo Steve
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The Combustion Process of the TDI Engine
In the direct injection diesel engine, fuel is injected directly into the main combustion chamber, unlike other diesel engines which use a preliminary intake chamber. This results in a more efficient combustion and lower fuel consumption for the Turbo Direct Injection engine.
The TDI's intake port, pistons, and injectors have all been specifically designed to optimise the combustion process, with respect to noise emission and running characteristics.
Inlet Swirl Port
The intake port is shaped in such a way that it induces a swirling movement of the intake air, and as a result, produces greater turbulence in the combustion chamber within the piston's recess.
Piston Recess
The shape of the piston recess encompasses most of the combustion chamber and has been optimised specifically for the newer TDI engine.
5-Hole Two-Stage Injector
The diesel fuel is injected into the piston recess area in two separate stages as the compressed air accelerates to a high enough temperature to ignite the fuel. This way, the two-stage injection process avoids a sharp pressure rise and keeps the explosion sounds to a minimum.
The 4 Stage Combustion Process
1. Intake Stroke
When the piston is at TDC (Top Dead Center), it can only move in a downward motion - creating a vacuum that sucks or pulls air through the open intake valve and into the cylinder.
2. Compression Stroke
When the piston is at or near BDC (Bottom Dead Center), the intake valve closes and the piston starts its upward climb to the top - compressing the intake air 19.5 times its prior volume. As the piston reaches its peak upward movement, the compressed hot air reaches approximately 750* F. - just as a fuel injector sprays a small stream of diesel fuel into the combustion that instantly ignites the air fuel mixture.
3. Power Stroke
The immense heat and pressure from the explosion within the combustion chamber powerfully drives the piston down with such force that its momentum twists or turns the crankshaft and three other pistons with it.
4. Exhaust Stroke
The momentum that the piston received from the "power stroke" also carries it back up to the top, as the exhaust valve opens and the piston drives out the spent gasses into the exhaust manifold. When the piston reaches TDC again, it is in position to repeat this 4 - cycle combustion process all over again, starting with the Intake Stroke.
Note: A small portion of VW's Technical Data Sheet on http://www.vw-industrieverkauf.de/englisch/index.htm contributed to this post.
[This message has been edited by Turbo Steve (edited February 14, 2000).]
In the direct injection diesel engine, fuel is injected directly into the main combustion chamber, unlike other diesel engines which use a preliminary intake chamber. This results in a more efficient combustion and lower fuel consumption for the Turbo Direct Injection engine.
The TDI's intake port, pistons, and injectors have all been specifically designed to optimise the combustion process, with respect to noise emission and running characteristics.
Inlet Swirl Port
The intake port is shaped in such a way that it induces a swirling movement of the intake air, and as a result, produces greater turbulence in the combustion chamber within the piston's recess.
Piston Recess
The shape of the piston recess encompasses most of the combustion chamber and has been optimised specifically for the newer TDI engine.
5-Hole Two-Stage Injector
The diesel fuel is injected into the piston recess area in two separate stages as the compressed air accelerates to a high enough temperature to ignite the fuel. This way, the two-stage injection process avoids a sharp pressure rise and keeps the explosion sounds to a minimum.
The 4 Stage Combustion Process
1. Intake Stroke
When the piston is at TDC (Top Dead Center), it can only move in a downward motion - creating a vacuum that sucks or pulls air through the open intake valve and into the cylinder.
2. Compression Stroke
When the piston is at or near BDC (Bottom Dead Center), the intake valve closes and the piston starts its upward climb to the top - compressing the intake air 19.5 times its prior volume. As the piston reaches its peak upward movement, the compressed hot air reaches approximately 750* F. - just as a fuel injector sprays a small stream of diesel fuel into the combustion that instantly ignites the air fuel mixture.
3. Power Stroke
The immense heat and pressure from the explosion within the combustion chamber powerfully drives the piston down with such force that its momentum twists or turns the crankshaft and three other pistons with it.
4. Exhaust Stroke
The momentum that the piston received from the "power stroke" also carries it back up to the top, as the exhaust valve opens and the piston drives out the spent gasses into the exhaust manifold. When the piston reaches TDC again, it is in position to repeat this 4 - cycle combustion process all over again, starting with the Intake Stroke.
Note: A small portion of VW's Technical Data Sheet on http://www.vw-industrieverkauf.de/englisch/index.htm contributed to this post.
[This message has been edited by Turbo Steve (edited February 14, 2000).]
