High crevice volume in a diesel engine is said to influence which emissions according to the technicians?

• A. Technician A: particulates
• B. Technician B: NOx
• C. Both Technicians
• D. Neither Technician A nor Technician B

Answer: (D)

High crevice volume creates a small, recessed space around the piston rings and related areas where part of the air–fuel mix can become trapped. That pocket has a high surface-to-volume ratio, so heat is conducted away to the walls and combustion in that region can be incomplete. Because emissions depend on a mix of factors—how fuel and air mix, when injection occurs, engine load, temperature, and how thoroughly the soot can be oxidized—the effect of this crevice volume is not a simple, one-way influence on a single emission.

Particulates (soot) tend to increase when there are regions of incomplete combustion, but NOx formation depends mainly on peak temperatures and the oxygen availability during combustion. The cooling effect from crevice walls can lower peak temperatures (potentially reducing NOx) while the localized rich pockets can promote soot formation. Because the net effect varies with design and operating conditions, it isn’t accurate to claim that high crevice volume universally influences one emission category more than another based on these technician statements.

So, in this context, neither technician’s claim can be considered universally correct, making the most accurate answer that neither statement uniquely applies.