Starting a diesel engine with injected compressed air uses approximately which pressure?

• A. 520 kPa
• B. 2100 kPa
• C. 255 kPa
• D. 3030 kPa

Answer: (B)

Starting a diesel engine with injected compressed air relies on delivering a high-pressure air charge into the cylinders to push the pistons and turn the crank until the engine can run on its own. The air must be dense enough to fill the cylinder and overcome friction and the compression starting from rest. In practice, starting air is supplied at about 20 bar (roughly 2 MPa). The option around 2100 kPa (about 21 bar) matches that typical starting-air pressure, making it the best estimate. Pressures much lower would not provide enough starting torque, while a much higher pressure is generally unnecessary for starting and may exceed typical system ratings.