So I asked Autoline TV about diesels

I watched 10-15 minutes after your question was presented, Bob.

They make some good points, but I disagree with a few (that I saw):

- the expense of bringing LD diesel vehicles into compliance with Tier 3/LEV 3 is already "baked into the cake." All LD diesel vehicles currently on the market in the U.S. have SCR for NOx emission control. It can be very effective as demonstrated by CARB itself (2015 VW TDIs "after repair" have NOx emissions near SULEV levels, according to a graphic on their web page).

Also, many if not all direct-injection gasoline vehicles (GDI) will probably require particle filters (GPF), or should at least, when Tier 3/LEV 3 is full implemented. That will likely increase their cost at least somewhat and may even degrade mileage a little.

- I'm not convinced the fuel efficiency gap between gas and diesel have been close as much as implied in that discussion. They cite the Equinox as not having a significant difference between the diesel and the 1.5 gas versions. However, the official overall difference between the diesel and gas versions of all vehicles in which both are available (2017 model year) is about 32% based on my calculation (hopefully correct). The often-stated advantage of diesel over gas is 30% and has been for a couple of decades now.

Also, if you take the BMW 3-Series as an example, the gap between the diesel version (328d) and the nearest equivalent gas version (320i) is about 30% officially. In Fuelly, the "real-world" gap is almost 45%.

I acknowledge that hybrids are generally better for urban driving, but diesels still can be advantageous for some driving conditions.

 

Are there problems making a diesel hybrid? Or is it just kind of pointless, no significant advantage?

 

Apparently, full diesel hybrid is too expensive for the fuel mileage benefit.

Looks like "mild hybrid" (48-volt systems) is better suited for diesels:

Green Car Congress: Continental puts first 48V hybrid assist system into production with Renault diesels


Advanced ADEPT 48V affordable hybrid on path to meet future ultra-low vehicle emissions - Global engineering, environmental and strategic consultancy

 

Thank you Bob.

Have you looked at the "unrounded" adjusted fuel mileage ratings for the Equinox diesel (Download Fuel Economy Data - "2018 datafile")?

The AWD diesel version actually has incrementally better combined fuel mileage than the front-wheel drive version (31.82 mpg for the AWD; 31.78 mpg for the FWD).

 

There was a two-cylinder, 730 cc two-cycle diesel engine being developed by Renault (Could Our Cars Get Two Stroke Diesels? - Engine Builder Magazine) for such applications. Renault claimed 50% efficiency (5th paragraph).

Haven't heard any more about it since 2015 though.

 

It's mostly about cost. Hard enough to get car buyers in America to consider a hybrid or diesel because of that higher price.
Then the gas hybrids have good fuel efficiency because the ICE is a low power Atkinson version. The low torque of electric motors matches up to the ICE quite well. Diesels, on the other hand, are already good on the low end torque front. The cost of a full hybrid system won't bring as much gains to the diesel.