I think that it is a natural question to ask why automakers haven't made a diesel electric-hybrid vehicle yet. With diesels offering great fuel efficiency, and hybrids offering the same, it seems as though a diesel electric-hybrid would be an extra efficient vehicle. Volkswagen in particular has been trying to promote diesel in the US, so it would seem like the perfect company to go forward with the first diesel electric-hybrid vehicle. I think the first thing to consider is what the goals of a hybrid vehicle are.
I'd say that there are three main goals of hybrid vehicles. The first and foremost goal of hybrid vehicles is to increase fuel efficiency. The higher the MPG rating, the better. The second goal would be being environmentally friendly. This would be measured by CO2 emissions. And the final goal of hybrid vehicles would be to reduce the cost of ownership. Now, let's see how a diesel-hybrid would do in reaching these goals.
Right off the bat, let me point out that there is no diesel car in the US market that is the fuel efficiency leader in its class. Gasoline vehicles are more efficient when looking at what is currently available in the market. Such a fact makes the idea of having an uber efficient diesel-hybrid seem like less of a possibility, and more of a pipe dream.
When one looks at how diesels do with CO2 emissions a similar conclusion is reached. Diesel powered vehicles, even with new regulations that have narrowed the gap, still produce more CO2 emissions per mile than gasoline cars. That means that if you take any diesel and compare it to a gasoline counterpart, the gas-powered version will undoubtedly do less harm to the environment.
Then we come to cost of ownership. Many hybrid buyers are looking to spend less on fuel over the course of their vehicle's life. With diesel fuel costing 20% more than gasoline on average, owning a diesel would be more expensive than a petrol powered car. In order for a diesel to save you money it would have to be more fuel efficient than a petrol powered car by a significant margin to make up for the higher price of diesel. On top of that, diesel vehicles offered by car makers are always priced higher than their gasoline powered counterparts, which again adds to cost of ownership.
Benefits to having a diesel hybrid just aren't significant enough to make up for the shortcomings I've discussed above. Added torque isn't that substantial since electric motors provide great torque in gasoline-hybrid vehicles, and the current trend towards turbocharged gasoline engines also offer lots of torque.
The other benefit is better highway fuel economy. This is true, but when stacked up against the other things discussed above it just doesn't do enough to justify the creation of a diesel hybrid.
So that is why VW is coming out with a Golf GTE hybrid, but no Diesel Golf GTE hybrid. Do you see any circumstances that would be prime for a diesel hybrid vehicle?