GM Study Shows 10% Improvement in Fuel Economy Along With Reduction in Criteria Emissions from Mild Hybridization of 4-Cylinder Diesel

Applying a production-intent second-generation GM Hybrid System (High Voltage Belt Alternator Starter—BAS) to a 4-cylinder common rail diesel can yield fuel economy improvements of up to 10%, as well as reductions in the emission of criteria pollutants, according to Maurizio Cisternino, GM Powertrain Europe Advanced Engineering Hybrid Innovation Manager.

In a presentation at the US Department of Energy’s 2010 Direction in Engine-Efficiency and Emissions Research Conference in Detroit (DEER), Cisternino described the results of an internal study that used both testbed experimental engine work as well as vehicle tests using an Opel Corsa equipped with a BAS-enhanced 1.3-liter diesel 95 hp Euro 5 engine with manual transmission.

GM 2nd Gen BAS
Operating voltage ~115
Power ~15 kW peak
Torque ~65N&iddot;m
Engine-motor coupling ratio 2.4:1
Battery capacity 5.5 Ah

Engine operation at the dynamic test bed was performed on a 1.3-liter diesel as well as a 1.9 liter Euro 4 diesel.

The activities were designed to investigate the optimization of hybrid control and calibration strategies targeting:

  • Start/stop functionality (electric motor control for engine spin up and spin down ramp profile, fuel injection schedule calibration, throttle calibration for next NVH and cranking time consistency);
  • Start/stop activation strategy with optimized clutch-based control;
  • Enhancement of vehicle transient performance (launch/elasticity) through BAS torque/power assist; and
  • Drivability subjective assessment in coast and brake regeneration modes, electric boost, clutch/gear shift at full e-boost, and transition from start mode to idle.

Bench testing showed a general improvement of CO and HC emissions due to the decrease of engine idling time (pre-Cat CO and THC reduction of 16% and 9% respectively) and to accelerated DOC light-off leading to substantial downstream CO and THC reduction (78% and 18%, respectively). The reduction of both engine out and tailpipe emissions was due to lower generation and quicker DOC light off (caused by higher gas temperatures by suppressing idling), Cisternino said.

NOx emissions also improved 13% if EGR functionality is well mated to the hybrid functionality. Electric assist during transients contributed to the moderate NOx decrease. PM engine-out emissions are unaffected by mild hybridization.

Vehicle tests showed a cranking time of 435ms (from 0 rpm to idle) with a spread of 55ms depending upon the engine stop position; very low NVH, 13% elasticity improvement; and an overall positive rating in drivability.

Future testing will evaluate the synergies of mild hybrid technology with a turbocharger for optimal turbomatching; a valve deactivation mechanism for energy recovery enhancement; lower temperature EGR and Euro 6 aftertreatment strategies (SCR, LNT) to improve conversion efficiency and to support efficient DPF regeneration).


  • Maurizio Cisternino (2010) Influence of Mild Hybridization on Performance and Emission in a 4-Cylinder In-Line Common Rail Diesel Engine (DEER 2010)

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