An embedded system based control strategy for no_x reduction in diesel-cng engines

Nitrogen Oxides (NOx) are major air pollutants from diesel engines. Engines that operate on more than one fuel source (as in Diesel-CNG engines) are gaining popularity because they provide a relatively easy and inexpensive alternative which reduce NOx emissions by reduced use of diesel fuel. However, such Diesel-CNG based Dual-FuelTM engines still produce significant NOx exhausts under certain driving conditions. A proven technology for reducing NOx from diesel engine exhausts is the Selective Catalytic Reduction (SCR) process.

This paper describes the design and development of an embedded system based control strategy for Diesel-CNG Dual-Fuel™ systems using SCR technology. The developed strategy is designed to work in tandem with the existing Diesel-Specific NOx control strategy to meet the emission targets. It is implemented in an Electronic Control Unit (ECU) that controls the SCR system for NOx reduction. Based on the information available from different sources (via CAN, analog sensors and internally calculated parameters), a closed loop control strategy is developed with a simplified model of the system dynamics (including SCR chemical reaction dynamics). The strategy determines the amount of AdBlue® needed for dosing by the dosing valve of the SCR system. The system is also designed with the flexibility to switch to an open-loop control strategy, or user control inputs. The developed strategy was integrated to work in tandem with the company proprietary Diesel-only Mono-Fuel NOx reducing strategy. This enables both the strategies to work in a single Denoxtronic® ECU environment which can be used either for Mono-Fuel or Dual-Fuel™ engines.

The developed strategy for Diesel-CNG engines was benchmarked, under diesel-only operation, against the existing diesel Mono-Fuel strategy. In spite of the simplified model dynamics, the developed strategy was able to perform like a Mono-Fuel strategy by capturing the coarse control dynamics and the results obtained converges to the Mono-Fuel strategy.