- Diesel Engine Tips page 5 - by P B Gill
All most all the newer diesel engines now use a turbocharger to increase the power . With the use of a turbocharger , the base compression of the engine can be much lower . An example of this would be , a non turbocharged engine would normally have a compression ratio of 21 to 1 or higher . The same engine but with a turbocharger could have the compression ratio lowered to 17 to 1 or in that range . This lower compression means the engine will be easier for the starter to turn over when starting the engine . Lower compression also puts less load on the pistons and connecting rods etc , during idle , while cruising and on deceleration .
A turbocharger had two sections , an exhaust side and a compressor side (also called a fresh air side) .
_
Diesel engines control the amount of fuel fed through the fuel injectors and into the engine cylinders to control the speed that the engine turns and to control the amount of power that the engine produces . (gasoline engines control the amount of fresh air that is fed into the engine to control the speed of the engine and the power it produces) . As more fuel is allowed through the diesel fuel injectors and into the cylinders of the diesel engine , the more power is produced and the faster the engine turns . As the engine turns faster more exhaust pressure is produced and the faster the turbocharger turns .
Exhaust from the engine is routed through the exhaust side of the turbocharger and the exhaust pressure turns an impeller (fan) which drives the compressor (fan) in the fresh air side of the turbocharger . The faster the turbocharger turns the more fresh air the compressor forces into the engine cylinders. The more fresh air that is forced into the cylinders , the more air is expanded by the heat of combustion to produce the increase of power in the engine .
_______
The first turbochargers were used often on smaller engines to boost power only on acceleration . They were not very efficient and required a lot of maintenance to keep them operating properly . They were often very slow to respond and caused hesitation of the engine before they began to boost .
Today’s turbochargers are very efficient and very durable and require no maintenance . Keep the air filter clean and securely in place , and keep the engine oil clean and the turbocharger will last a long time .
Most turbochargers today are fully functional . This means that they supply boosted fresh air pressure to the engine at all times , except at idle and when decelerating . As soon as you press the accelerator pedal down , the turbocharger begins to boost the fresh air pressure into the engine . At light throttle (when you press the accelerator lightly) the boost pressure is likely about 1 to 3 pounds . This means that there is 1 to 3 pounds of pressure pushing fresh air into the engine cylinders . As you press the accelerator harder the boost pressure is increased and can normally reach a pressure of about 13 to 18 pounds (depending on the vehicle) during maximum acceleration . Turbochargers only boost what is needed by the engine and only when it is needed . This helps to eliminate unneeded stress on the engine and helps to prolong its life . Turbochargers are also controlled by the power train control module and by a waste gate on a butterfly valve , mainly to protect against over boosting at the improper time . If the power train control system senses excessive boost it will open a waste gate to dump off exhaust pressure to lower and control the amount of boost . When a buttery fly valve is used , the valve can be closed and opened by the power train control system to control the amount of boost . Butterfly valves (were used) will often be closed when the engine is cold , the help heat the engine up more quickly .
