Combustion system optimization for FCA 1,6l diesel engine

A completely new combustion system has been developed for the FCA 1,6l 4 cylinder diesel engine in order to improve engine-out emissions and fuel economy. New combustion system development has been carried out by performing experimental activities at single cylinder engines (both optical and metal single cylinder) and 3D CFD simulations. The best configuration has been finally assessed at the engine test bench obtaining relevant improvements in terms of emissions and specific fuel consumption.

The main criteria for defining the new combustion system was the reduction of air motion within the combustion bowl with the goal to minimize the thermal losses and so to improve the combustion efficiency. However, low air-motion deteriorates the air to fuel mixing thus producing an increase of smoke emission. For that reason, a specific nozzle with reduced hydraulic flow rate was designed to match with the new bowl in order to maximize the air utilization in the combustion chamber.

Through CFD 3D simulations several combustion systems, with both conventional and non-conventional bowl shapes, have been assessed.

Example : Temperature and Soot contour plots of variant 5 (tapered bowl shape)

The best two configurations have been finally tested on multicylinder engine where an enhanced EGR system with cooled High Pressure and Low Pressure circuits has been also applied to further reduce emissions and fuel consumption.

With the piston bowl Variant 6 a 3% benefit of BSFC (brake specific fuel consumption) average has been assessed.

Experimental results summary at part loads

At the same time, despite the reduction of the nozzle hydraulic flow rate, a good increase of the maximum rated power has been measured.

Finally, a complete engine calibration has been developed and the engine map measured. With respect to the baseline –current production engine- the new configuration clearly improved engine out emissions, specific fuel consumption and combustion noise.

The following results have been achieved at the same NOx emissions on most of the working points:

  • BSFC reduction > 3%
  • Combustion Noise reduction up to more than 2 dBA
  • Smoke reduction up to 0,6 FSN
  • HC reduction of more than 50%

Partners : CNR (optical single cylinder), CRF (simulations and multicylinder), IFPEN (metal single cylinder and simulations).