April 06, 2006
Diesel Hybrids Seen As Most Efficient But Most Costly

Technology Review has an article reviewing the prospects of diesel hybrid vehicles. PSA Peugeot CitroŽn has demonstrated a record efficiency diesel hybrid but the diesel and the hybrid both add to the total cost.

What's holding back commercialization is cost. A diesel-powered car in Europe already costs $1,750-2,400 more than an equivalent gasoline model, and PSA estimates that making a diesel hybrid could double that premium. Hence, PSA says controlling costs will be a challenge, but it is starting to engineer cost-shaving solutions.

Note that even in Europe with much higher gasoline prices the diesel hybrid is still seen as too expensive to justify the fuel savings.

But diesel hybrids would be more efficient than gasoline hybrids.

What's clear is that diesel hybrid technology has significant potential. According to a 2003 study by MIT's Laboratory for Energy and the Environment, a study that remains one of the most comprehensive projections for propulsion technologies, diesel hybrids should outperform nearly all other propulsion technologies through 2020 -- including fuel-cell cars that run on hydrogen derived onboard from gasoline. Fuel cells using pure hydrogen offered a marginal benefit in efficiency, but only when combined with hybrid technology, and at a significantly higher price.

But the hydrogen fuel cells only make sense if or when materials are found to store hydrogen at room temperature. If active air conditioning is needed to keep the hydrogen cold then cars will use energy even when stationary.

In theory fuel cells burning liquid hydrocarbons might surpass diesel engines in efficiency and would not suffer the hydrogen storage problem.

What will mature more rapidly? Battery technologies or fuel cell technologies? If battery technologies mature more rapidly then the world could move toward all electric vehicles. If fuel cells mature more rapidly then battery improvements could still get used in combination with fuel cells to power fuel cell hybrids. Batteries allow regenerative braking to capture energy that would otherwise be lost. Unless a fuel cell design can enable a non-battery dependent method of capturing the braking energy the role of battery-based hybrids seems set to grow even if fuel cells start competing with the internal combustion engine.

Technology Review has another article reporting on an advance at the University of North Carolina at Chapel Hill that may greatly reduce the cost of fuel cells.

Joseph DeSimone, the UNC-Chapel Hill chemistry and chemical engineering professor who heads the lab where the work was done, thinks they can increase the membrane's surface area 20 to 40 times by using different patterns, increasing the power density proportionately.

Such improvements in power density mean that a much smaller fuel cell could provide adequate power for a vehicle. The material is also easier to work with, which should reduce manufacturing costs.

They mention that these fuel cells might work well with methanol. I'm guessing the fuel cell cost problem is going to get solved before the hydrogen storage problem. So initial vehicle fuel cells are probably going to burn liquid hydrocarbons.

Share |      Randall Parker, 2006 April 06 09:56 PM  Energy Policy

PacRim Jim said at April 7, 2006 1:00 AM:

The fine diesel particles go so deep into one's lungs that they cannot be eliminated by the lung. Decade after decade they irritate, sometimes leading to lung cancer. Now is diesel so appealing?

AA2 said at April 7, 2006 5:26 AM:

That fuel cell breakthrough seems potentially huge. Btw I agree with you Randall about hydrogen. I always like the idea of just running gasoline through the fuel cells for more efficiency.. Instead of going for an exotic fuel like hydrogen.

I wonder if this helps total power output to the wheels? Instead of making a smaller cell, make one of similiar size but much more powerful?

Paul Dietz said at April 7, 2006 5:46 AM:

PacRim Jim: synthetic diesel fuels have lower particulate emissions. Filters can capture almost all of what's left, and I bet a diesel in a hybrid configuration can be programmed to operate away from the off-nominal, high load conditions that generate the most soot (use the battery to provide the burst in those situations.) This would all have a cost impact, admittedly.

The thing that would concern me most is NOx emission, but presumably one could do something similar to the Atkinson cycle engine in the Prius where the valves are timed to make the expansion stroke longer than the compression stroke. This would increase efficiency (at the expense of maximum power) while limiting peak temperature.

odograph said at April 7, 2006 7:06 AM:

For what it's worth, I saved this great table of Well To Wheel efficiencies a while back:

http://odograph.com/data/2005/04/02/table81.png (link)

It comes from this pdf:

http://www.iangv.org/jaytech/files/Pathways_Part_A.pdf (link)

It does rank a diesel hybrid as #1, and interestingly a CNG hybrid as #2.

hamerhokie said at April 7, 2006 11:08 AM:

I think any new configuration, be it battery or fuel cell, will include a way of capturing regenerative braking energy, especially with the fast-recharge batteries on the way.

It's going to be very hard to pick a winner but I would place my money on whatever technology has the potential to attract unreasonably high government subsidies.

Rob said at April 7, 2006 12:15 PM:

Well, batteries aren't so great, but probably the best recapture will be ultracapacitors using nanotech to massively increase the surface areas of the plates.

Wolf-Dog said at April 7, 2006 11:27 PM:

Note that according to the article, until 2020 such hybrids won't even be close to replacing the ordinary wasteful cars, and the global oil demand will increase dramatically by then.

This means that the nations of the world will be at each other's throats, and it will be a fight to the death. Since I was raised as a house dog, I am against reviving my wolf genes, and so it is my hope that the Lithium batteries will be sufficiently improved within 3 years. If only we double the efficiency of the current Lithium batteries, we can quickly switch to pure electric cars.

Moldy said at April 8, 2006 8:48 PM:


The CNG diesel in that article I suspect is from Westport Innovations of British Columbia Canada. They have basically taken the diesel and run it on NG. With no power loss or Torque!!

In all electric vehicles where does one get heat from? Especially in -10F such as Canada.

Kurt watson said at December 10, 2007 12:10 PM:

Lithium batteries will be sufficiently improved as stated, but the electric charging will be the big factor. I am looking forward to the new "flex printed" solar films currently in R&D that are flexible (can be form fitted), cheap and easy to install. Then charge would come from your home solar source. The car of the future(sooner than you think)is achievable now. The successful electric car company could offer the 'solar kit' for the novice in a package deal. With a 500 mile range, the combo would take care of 90% of the American drivers.

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