🔍 Key Concepts

• Diesel engine indicator (P–V) diagram for a four-stroke cycle • Where in the cycle fuel injection starts relative to top dead center (TDC) and the compression stroke • Difference between compression line and combustion/expansion line on a P–V diagram

💭 Think About

• Identify which labeled point is closest to top dead center at the end of the compression stroke just before pressure rises sharply • Trace the direction of the arrows along the cycle and decide where the line changes from compression to rapid pressure increase at nearly constant volume • Compare each option (c, d, e, f) with where you would expect injection to begin in a real diesel engine (slightly before or right at TDC)

✅ Before You Answer

• Verify which vertical dashed line (A or B) represents top dead center for this cylinder event • Confirm the direction of rotation around the diagram so you know the order: intake → compression → combustion/expansion → exhaust • Check that the point you pick lies at the transition between compression and combustion, not during pure compression or later expansion