- Carbureted systems
- Electronic fuel injection systems
- Diesel induction systems
- Exhaust systems
Carbureted systems
On a carbureted engine, the intake system is part of the fuel system.
The main function of the intake system on a gasoline engine is the delivery of the required amount of the mixture of air and fuel.
In a basic system, air enters the air cleaner for filtering, then passes into the carburettor, where it mixes with the required amount of fuel. This air-fuel mixture then enters the intake manifold, and finally the cylinder.
The same basic principle applies on the rotary engine.
On all carbureted systems, the intake system can be crucial in increasing engine output. This can be done by increasing volumetric efficiency, that is, by increasing the amount of air-fuel mixture burned in the cylinders.
This can be achieved by using a larger inlet valve to admit more charge into the combustion chamber; by using large, free-flowing intake manifolds; or by using extra carburetors.
Carbureted intake systems were once standard for gasoline engines, but increasingly they are being displaced by electronic fuel injected systems.
Electronic fuel injection systems
The intake system is part of the fuel system. Its main function on a gasoline engine is to deliver the required amount of air-fuel mixture. Air is filtered by passing through an air cleaner.
Information from many parts of the engine are fed into an electronic control unit, which then determines how much fuel should be injected for those exact conditions.
Pressure from an electric pump supplies fuel to electrically controlled injectors.
There are two basic electronic fuel injection systems. - single-point, and multi-point.
In the single-point system, the intake manifold carries an air-fuel mixture. Fuel is sprayed into the top-centre of the intake manifold. This manifold is the same as on a carbureted system.
In a multi-point system, the intake manifold carries air only. Multi-point injection has a fuel injector in each inlet port going to each cylinder. Gasoline is sprayed into each port, toward each intake valve.
The intake system can be crucial in increasing engine output. This can be done by increasing volumetric efficiency, that is, by increasing the amount of air-fuel mixture burned in the cylinders.
In fuel injection systems, this partly occurs automatically because of the increased efficiency of fuel injection compared to carbureted systems. Output can also be improved by using large, free-flowing intake manifolds, and by using larger valves to admit more charge into the combustion chamber.
Another method uses forced induction or supercharging.
Diesel induction systems
The two main components of the 4-stroke intake system are the air cleaner and the intake manifold.
But in a diesel engine, fuel is delivered separately and the intake system carries air only.
Also, since the diesel engine doesn’t have a carburetor, it has no throttle. Some diesels use a pneumatic governor with a butterfly valve at the entrance to the inlet manifold
Diesel engines often have more than one air cleaner.
Let’s look at the intake system for a 2-stroke diesel engine. There is only a very short time at the end of its power stroke to scavenge the exhaust gases and refill the cylinder with air. To achieve this in the time available, 2-stroke diesels use an engine-driven air pump, usually called a blower. It pressurizes the air so that when the inlet ports open, air from the blower enters the cylinder and helps scavenge the exhaust gases.
Some 2-stroke diesel engines use a turbocharger which feeds air under pressure to the blower.
The intake system of the diesel engine can be used to increase engine output. This can be done by increasing volumetric efficiency, that is, by increasing the amount of air-fuel mixture burned in the cylinders.
In diesel injection systems, this partly occurs automatically because of the increased efficiency of fuel injection.
Output can also be improved by using large, free-flowing intake manifolds, and by increasing the number, or the size, of inlet valves per cylinder to admit more charge into the combustion chamber.
Another method is to use forced induction or supercharging.
Exhaust systems
During engine operation, each time the exhaust valve opens, pulses of hot exhaust gases are forced into the exhaust manifold. These hot, rapidly expanding gases produce a lot of noise, some of it at very high frequency.
The exhaust system does several jobs. It has to reduce the noise of the exhausting gases to acceptable levels.
It has to discharge the gases safely, far enough away to prevent them re-entering the vehicle.
Some of these gases are highly poisonous. In an enclosed space, carbon monoxide can cause death in minutes. It is odorless and colorless, which makes it difficult to detect, and removing it is especially important.
In modern vehicles, it also keeps harmful emissions to a minimum.
The exhaust system is designed to enhance engine operation. A well-designed system can improve drivability and performance.
In this simplified model, burned gases exit the cylinder through the exhaust port and pass into the exhaust manifold.
The first pipe is usually called the engine pipe. It is connected to the outlet of the manifold which carries the exhaust gases to the muffler, which reduces exhaust noise.
Exhaust gases are then discharged through a tail pipe, usually at the rear, or sometimes, to the side or above the vehicle.
