The Key Role of the Closed-loop Combustion Control for Exploiting the Potential of Biodiesel in a Modern Diesel Engine for Passenger Car Applications 2011-37-0005

The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the capability of GM Combustion Closed-Loop Control (CLCC) in enabling seamless operation with high biodiesel blending levels in a modern diesel engine for passenger car applications. As a matter of fact, fuelling modern electronically-controlled diesel engines with high blends of biodiesel leads to a performance reduction of about 12-15% at rated power and up to 30% in the low-end torque, while increasing significantly the engine-out NOx emissions. These effects are both due to the interaction of the biodiesel properties with the control logic of the electronic control unit, which is calibrated for diesel operation. However, as the authors previously demonstrated, if engine calibration is re-tuned for biodiesel fuelling, the above mentioned drawbacks can be compensated and the biodiesel environmental inner qualities can be fully deployed.

In order to enable such calibration re-tuning, it is fundamental to achieve a reliable biodiesel blending detection, and to use it for real-time combustion optimization, chiefly by optimizing the injection train. Therefore, the authors investigated the capability of CLCC to detect biodiesel blending ratio on the recently released 2.0L Euro5 GM diesel engine equipped with embedded pressure sensors in the glow plugs.

Various blends of biodiesel were tested, notably 20% by volume (B20), 50% (B50) and pure biodiesel (B100). Tests on the multi-cylinder engine were carried out in a wide range of engine operating points for the complete characterization of the biodiesel performance in the NEDC cycle.

The results demonstrated the successful capability of the CLCC control to detect biodiesel blending with reasonable accuracy and to implement the corrective actions to avoid emission drift and performance losses.