Final answer:
In ashless dispersant (AD) oils, the dispersant c. prevents carbon buildup by keeping particles and contaminants in suspension, thus maintaining engine cleanliness and efficiency.
Step-by-step explanation:
In ashless dispersant (AD) oils, the dispersant performs the function of preventing carbon buildup. Dispersants are additives in lubricants like engine oils that help to keep contaminants and particles in suspension. This avoids the agglomeration or clumping of these particles which can lead to sludge and carbon deposits. It's important because such buildup can reduce engine efficiency and cause wear. The dispersant keeps ingredients dispersed and maintains the cleanliness of engine parts by preventing deposits from forming and settling on surfaces.