2 Responses

1. Manufacturers really can make anything they want since they have the R&D and know-how on these products. building a diesel hybrid is as simple as replacing the petrol engine in the prius with a diesel one. However, There is a lot of politics involved in this. America as a country, gets the lowest price per gallon than any other country in the world from a customer standpoint. That is because they are the largest customer and can get away with better discounts/bargains than others. However, to remain the biggest consumer, they cannot allow the common man to have vehicles that suddenly start using only half the amount of oil that they now do. It would hurt the oil companies too much. Even the ones producing and operating inside America.
   This is not such a big deal in countries like india and european ones since they do not get such great prices per barrell anyway. So they have no choice but to choose alternatives to petrol like Diesel, as they already have.
   This is only one explanation to your question. There are theories about greater pollution being caused by using diesel etc that also play their part.
   Also, a diesel engine is supposed to cost more in maintenance since the whole process is dirtier than a petrol engine. Carbon formation and engine sludge problems are greater in diesel engines than petrol. However, these are not problems that cannot be fixed by some R&D.
   Hope that answers your question.

2. The short answer is yes..they can be built. Trains have used them for years. The problem is burning diesel has more pollutants, the engines are heavier and cost much more to design, engineer and produce than an existing gas engine which can be quickly converted to a hybrid vehicle rather than designing a whole new engine for a car or truck. And diesel fuel prices can fluctuate a lot more than gas because of more demand at times for home heating oil…which is the same as diesel…demand from shipping via semi-trucks or increased use in spring and fall for farmers planting and harvesting. The US car and light truck fleet has always been more geared to gas engines with low fuel prices so it would take a major investment in developing diesel’s like European countries and some others do. Car companies usually don’t want to invest in anything that doesn’t have a high probablility of paying off. With the new low-sulfur content laws being passed, it could make diesel fuel cars more attractive in many regards but the higher price at the pump could offset this.