In a four-stroke cycle diesel engine, the intake valve starts to open at _____.

Explanation:

Four-Stroke Cycle Diesel Engine

Definition: A four-stroke cycle diesel engine is an internal combustion engine that operates on the diesel cycle, completing a power cycle in four strokes of the piston: intake, compression, power, and exhaust. Diesel engines use compression ignition to burn the fuel, which is injected into the combustion chamber.

Working Principle: The four strokes of a diesel engine are:

• Intake Stroke: The intake valve opens, and the piston moves down from the top dead center (TDC) to the bottom dead center (BDC), allowing air to enter the cylinder.
• Compression Stroke: The intake valve closes, and the piston moves up from BDC to TDC, compressing the air inside the cylinder. The temperature and pressure of the air increase significantly.
• Power Stroke: Near the end of the compression stroke, diesel fuel is injected into the cylinder, and the high temperature and pressure cause the fuel to ignite. The resulting combustion forces the piston down from TDC to BDC, generating power.
• Exhaust Stroke: The exhaust valve opens, and the piston moves up from BDC to TDC, expelling the combustion gases from the cylinder.

In a four-stroke diesel engine, the intake valve begins to open before the piston reaches Top Dead Center (TDC) on the exhaust stroke. This early opening, typically 10°−25° before TDC, ensures that the valve is fully open when the intake stroke begins, allowing optimal airflow into the cylinder. This timing is part of the engine's valve lead for efficient scavenging and charging.