Which statement is correct about soot in EGR systems?

• A. All EGR systems contain soot
• B. Caterpillar's Clean Gas Induction system does not contain soot
• C. Soot is never present in EGR gas
• D. Soot presence is unpredictable

Answer: (B)

Soot in EGR systems depends on how clean the gas entering the engine is. Some designs include filtration or a separate clean-gas path that removes soot before any exhaust gas is recirculated, so the EGR flow can be effectively soot-free.

That’s why the statement about Caterpillar’s Clean Gas Induction system is correct: this design is built to deliver gas that is free of soot, meaning the EGR portion in this system does not contain soot.

The other ideas aren’t generally true. Not every EGR system has soot, and soot can be present in EGR gas in many designs unless there’s dedicated filtration or clean-gas induction. Saying soot presence is unpredictable ignores how engineering choices control contamination.