An engine manufacturer specifies a fuel injection timing advance of 18 degrees Before Top Dead Centre (BTDC) for optimal performance. If the engine is currently operating with an injection timing of 15 degrees BTDC, what effect might this have on engine operation?

Question: An engine manufacturer specifies a fuel injection timing advance of 18 degrees Before Top Dead Centre (BTDC) for optimal performance. If the engine is currently operating with an injection timing of 15 degrees BTDC, what effect might this have on engine operation?

Answer options:

• Increased NOx emissions and slightly improved fuel economy. ✅ Reduced power output and increased black smoke (soot).
• Increased idle stability and reduced engine noise.
• Higher cylinder pressures and increased engine knocking.

Correct answer: Reduced power output and increased black smoke (soot).

Explanation: Retarded injection timing (15 BTDC instead of 18 BTDC) means fuel is injected later in the compression stroke, leading to less time for complete combustion and lower peak cylinder pressures, resulting in reduced power output, increased fuel consumption, and higher particulate matter (black smoke) emissions.