EGR for petrol/gasoline engines

by Alex

Expert answer:

Quick answer

Petrol EGR also reduces NOx by mixing exhaust into the intake at partial load. It’s less crucial than in diesels—gas engines run cooler—but still helps manage emissions and can curb knock. Modern petrol EGR is often electronically controlled.

Detailed answer

While diesels are famous for EGR usage, many petrol (gasoline) engines also employ the strategy to reduce nitrogen oxide (NOx) emissions. Here’s the gist:

1. How It Works
Under partial load—like when you’re cruising or gently accelerating—the engine control unit (ECU) commands the EGR valve to let a measured amount of exhaust gas into the intake manifold. This inert gas lowers the amount of oxygen available and thus brings down peak combustion temperatures, where NOx forms.

2. Emission Control
Gasoline engines typically produce less NOx than diesels, but to meet ever-tightening emission rules, EGR remains a handy tool. By controlling temperature in the cylinder, you reduce NOx formation before the catalytic converter even steps in.

3. Knock Reduction
Another perk in petrol engines is deterring knock (aka pinging). High cylinder temperatures can cause spontaneous ignition of the air-fuel mix. By recirculating cooled exhaust gas, you keep combustion gentler, helping avoid that damaging pre-ignition. The ECU might allow more spark advance or leaner mixes without fear of knock.

4. Differences vs. Diesel EGR
– Less Soot: Petrol engines don’t create the same heavy soot as diesels, so the EGR valve faces fewer carbon-clogging issues.
– Sensor Integration: Modern petrol EGR setups are electronically controlled, often using a position sensor and integrating with other emission devices (like catalytic converters) to meet precise NOx targets.
– Less Prominent: In some petrol engines, EGR is minimized or absent if direct-injection and advanced catalytic aftertreatment handle most of the NOx load. But many still rely on a smaller EGR valve.

5. Maintenance
Petrol EGR valves can still get sooty or coated with oil vapor. But the risk of massive carbon buildup is lower than in diesels. Occasional EGR or intake cleaning might be needed if you see idle instability or codes like P0401.

Conclusion
Though more associated with diesels, EGR is also found in petrol engines, lowering NOx by adding a bit of exhaust gas into the intake at mid-range loads. It helps keep cylinder temperatures in check, curtails knock, and meets emission standards more easily. Typically less prone to heavy soot clogs than diesel EGR, it still benefits from periodic checks or cleaning to ensure everything runs smoothly and meets environmental guidelines.

Share This Post:

Contact us

Find us on:

Newsletter