Simulation of Urea-SCR Process Applied to Lean-burn SI Engines

Lean-burn combustion in SI engines can significantly reduce fuel consumption but NOx reduction becomes challenging because classic three-way catalyst (TWC) is no more efficient. Urea-SCR is then an interesting alternative solution because of its high NOx conversion efficiency without any additional fuel consumption.

The coupling between two SI lean-burn engines (stratified and homogeneous combustion) and a urea-SCR catalyst was simulated on the NEDC cycle. Simulation results showed that the SCR efficiency would comply with the limits required by future Euro 5/6 regulations. Associated urea solution consumptions were estimated thanks to a simplified model.

Finally, a comparison with a Diesel application was also made. It showed that the required amount of reducing agent remained significantly higher for SI lean-burn engines than for Diesel engine.