Different Types of Exhaust Valves

An exhaust valve is a small metal device located on the exhaust pipe of an engine. Its job is to prevent air and smoke from entering the engine. There are different types of exhaust valves, and each has its own specific purpose.

Here are four of the most common types:

1. The port-type exhaust valve opens when the piston reaches the top of the cylinder, letting air and smoke escape. This type is mostly used in gasoline engines.

2. The direct-injection (DI) exhaust valve opens as soon as the piston moves down into the cylinder, allowing air and fuel to mix immediately before exiting the engine. DI engines are more efficient than port-type engines because they can use more fuel with fewer emissions.

3. The double-overhead-cam (DOHC) exhaust valve opens two times during each cycle: once at TDC (top dead centre), and again at BDC (bottom dead centre). This allows for smooth power delivery and improved emissions control. DOHC engines are common in hybrid vehicles.

4. The variable valve timing (VVT) technology allows an engine to vary its exhaust valve opening according to fuel demand or temperature conditions. 

An exhaust valve is a device that helps the engine breathe better. It's a metal or plastic flap that opens and closes to allow air to flow out of the engine. The valves are on the air intake side of the engine.