Each time a gasoline engine is replaced by a diesel engine, consumption at equivalent performance is reduced by 20%.
I feel we should be clear that hybridization is interesting from a technological perspective, but it is and will remain very expensive, so its environmental benefits need to be studied closely.
If hybridization involves combining a gasoline and an electric engine, the benefits are comparable to those provided by substituting diesel engines for gasoline engines, except that one of these solutions is much less costly than the other. That’s why I believe there is no real advantage in developing hybrid gasoline engines in those parts of the world where diesel engines are well established. Only a hybrid diesel engine is attractive because it offers both benefits.
-Jean-Martin Folz, Chairman of PSA Peugeot Citroën
Gas hybrids have had very disappointing economy results (to be fair most of them have been tuned more to improve acceleration than to improve economy). Diesels are proven technology. Diesel Hybrids are are an ideal combination. Diesels love to run at a steady speed (such as in highway driving) and electrics are at their best in start and stop in town settings. The hybrid combination reduces NOx over a diesel (NOx emissions are at their worst during acceleration) and Carbon Dioxide over a standard Gas hybrid. Daimler Chrysler reported a $7500 Cost premium for their ESX3 Diesel Electric hybrid. How much are they paying per unit to move their SUVs?
Many hope to jump to the "Hydrogen Economy". Of course the only way to get Hydrogen is to split it from something else, which takes lots of energy and we have no infrastructure and its energy density is very low. We have a diesel Distribution network now. One more happy thought:
Combining the power of diesel engines with the efficiency of hybrid technologies can have terrific payoffs. Last year, MIT's Laboratory for Energy and the Environment produced a study (PDF) comparing total lifecycle energy efficiency and greenhouse emissions (including use, production, fuel production, and eventual disposal) of idealized advanced internal combustion, hybrid, and fuel cell vehicles. Diesel hybrids turned out to be much better than gasoline/gasoline-hybrid cars, and highly competitive with the best hydrogen fuel cell systems (even assuming optimistic fuel cell vehicle development). But the best hydrogen fuel cell vehicles will require entirely new hydrogen production, storage, and fueling facilities; reformed-gasoline fuel cells (which are more likely to be used, as they would not require the wholesale replacement of fueling stations) fared much worse.
World Changing:Diesel Electric Hybrids Now