Diesel Hybrids: Why They Don't Make As Much Sense As You Think
2014 Chevrolet Impala 2.5-Liter Four-Cylinder: Quick Drive
The new 2014 Chevrolet Impala is a big five-passenger family sedan, the largest one Chevy sells... Read More
- #4LEADERBOARD RANK
- 2905ARTICLES CONTRIBUTED
- 1958COMMENTS POSTED
Add to circle
Related Photo Galleries
-
2013 Hyundai Sonata Hybrid: Gas Mileage Test...
-
Volvo V60 Plug-In Hybrid Proves Popular...
-
2013 Dodge Dart Limited: Gas-Mileage Drive...
See more photos »
Also See
-
2013 Nissan Altima: 31-MPG Combined Rating For...
-
2012 Hyundai Accent SE: Quick Drive...
-
2012 Honda Civic Hybrid: Multi-Day Drive Review
See more video »
Volkswagen's line of TDI diesel cars has passionate fans.
Now that the company is launching the 2013 VW Jetta Hybrid, it will likely gain some hybrid advocates too.
But diesel and hybrid fans are very different groups, as the company's marketing surveys show.
So why couldn't Volkswagen simply add a hybrid system to its diesel, thereby getting the best of both worlds?
Many diesel fans have suggested just that, but there turn out to be valid reasons that automakers believe will largely keep diesels and hybrids separate.
In discussions with engineers from Volkswagen and other diesel makers, three main hurdles come to the fore:
(1) COST
First and foremost is the issue of cost. On average, a diesel engine costs about 15 percent more to manufacture than a gasoline engine of equal output.
Add to that the $1,000 or more for a high-voltage battery pack, power electronics, and one or two electric motor-generators, and you've created a very pricey powertrain indeed.
In European countries, where diesel fuel and gasoline can cost $7 to $10 a gallon, buyers will pay a considerable premium for more fuel-efficient cars.
That's less true in the U.S., where gasoline averages less than $4 a gallon--and where diesel fuel is often more expensive per gallon than gas.
And it's one of the reasons that diesel passenger cars pose a thornier equation in the States.
While their torquey driving characteristics make diesels appealing (just like electrics), the fact that both the cars and the fuel are more expensive makes the payback from diesel's greater fuel efficiency more challenging to compute.
(2) NON-COMPLEMENTARY TORQUE CURVES
Most hybrids, especially those from market leaders Toyota and Ford, use gasoline engines specially tuned to run on what's called the Atkinson Cycle.
This highly efficient tuning gives them maximum power output at the top of their range, but almost no torque at lower speeds.
That is perfectly complemented by a hybrid's electric traction motor, which develops peak torque at 0 rpm, neatly compensating for the gutless gas engine until it runs up to speed.
A diesel, on the other hand, produces all its torque down low--as does an electric motor.
That means a diesel hybrid should have boatloads of torque off the line, but may require extensive gearing to ensure highly efficient running at speed.
There's likely a more technical explanation of the relative power and torque curves of the three different sources, but we're not going to attempt it here.
(3) LESS IMPRESSIVE IMPROVEMENT
Finally, one of the reasons that hybridizing gasoline engines works well is that they're less fuel efficient to start with.
Gasoline engines convert 25 to 30 percent of a fuel's energy content into forward motion at the wheels; the rest is wasted as heat and noise.
By contrast, a diesel converts 30 to 35 percent of the fuel's energy into forward motion--hence the higher fuel efficiency figures.
But that leaves less "headroom" for improvement.
In the end, say diesel engineers, a diesel hybrid would add a very expensive electrified system to an already-expensive engine ... but produce a less impressive overall increase than in gasoline cars.
Aha, but you say, there are already three diesel hybrids on the market in Europe!
Well, that's true. But only one of them pairs the diesel engine and electric motor together into a single powertrain: the Mercedes-Benz E 300 BlueTEC Hybrid.
The other two--the Peugeot 3008 HYbrid4 and the Citroën DS5 Hybrid--are what is known as "through-the-road hybrids," meaning that they have one powertrain on either end.
Those two can use the electric motor alone for lower-speed trips, the diesel engine for high-speed travel, and combine for highest performance driving by transmitting power through all four wheels.
It's probably significant that Mercedes-Benz, which has sold diesels in the U.S. for many decades, has no plans to sell the world's sole diesel-electric hybrid powertrain here in the States.
We'll see how it does in Europe once it's been on sale for a year or two.
Meanwhile, we invite engine and powertrain engineers to weigh in on these issues.
Leave us your thoughts in the Comments below.
+++++++++++
Follow GreenCarReports on Facebook and Twitter.
Related Articles
-
Volvo V60 Plug-In Hybrid Proves Popular: Production Doubles In Europe
-
Next Mercedes-Benz C-Class Will Offer Diesel, Hybrid Options In 2014
-
2014 BMW 328d: Diesel Sport Sedan At New York Auto Show
-
2015 Audi A3 TDI Diesel Sedan Unveiled At NY Auto Show
-
New York Auto Show: Which Green Car Is Most Important?
-
Follow Us
On Facebook
Most Popular This Week
More »
Audi Startled By Tesla Sales Success? Deleted Press Release... 
Can Tesla Raise More Than $1 Billion On Soaring Stock Price? 
Four Used Plug-In Electric Cars To Avoid 
How Are Electric-Car Batteries Made? Photos From Nissan's New... 
Toyota Accelerates Switch To Lithium-Ion Batteries, Still Lags... Find Green Cars
Photo Galleries
More from High Gear Media
- Follow Us
Have an opinion?
And high-end cars are more prone to that sort of death as repair costs for major components (e.g. A/C, suspension, ABS components) are often quite breath-taking, even when the engine and transmission are quite functional when the vehicle is scrapped.
But that is nothing for a diesel engine. My mazda6 started breaking in at around 70,000 miles, and I expect to get at least half a million miles from it with the rigorous maintenance schedule.
Diesels don't even start to break in until 60,000 - 80,000 miles, and it is expected that the odometer will roll over several times during the lifetime of the engine.
The engines themselves are no doubt still reliable, thanks to ever improving production techniques, but they're often let down by short-lived ancillaries. It's little use having an engine that lasts half a million miles if you've had to pay for several expensive replacement parts in that time.
Maybe not here, but in Europe for example, mazda has had the mazda6 with a particulate filter available since 2005, and those engines are near-indistructible.
I know what I have and I know their quality; I do not need it proven to me, because I used to drive those cars every day as my daily driver, for years.
I have lived in the future.
Your Mazda6 may well have been impeccably reliable, but the briefest of looks at many an owners' forum is enough to see that incidents are hardly isolated - modern diesels are very complex indeed and expensive to fix when they go wrong.
Who here wouldn't want a 90mpg diesel hybrid car?
"By contrast, a diesel converts 30 to 35 percent of the fuel's energy into forward motion--hence the higher fuel efficiency figures."
Hmm... I am NOT sure that is "entirely" true. It is true that diesel has a higher compression thus producing energy at a slight higher efficiency point. But Diesel fuel also has more energy content than gasoline to start with on a per gallon basis...
I completely agree with Point #1 as the most important reason. Point #2 is also valid since #1 is dominating. If they aren't paired well, then why bother.
I think diesel is better paired in terms of "series" hybrid.
I think clean diesel might be a "good engine" for Volt's series configuration (with special cases for parallel application at higher speed in extended range mode). But that will make Volt even more expensive.
Since Cruze is coming with a diesel engine. If that does well, I don't see why GM can't put it in the next generation Volt.
However, with the diesel engine, it would be difficult to meet California's AT-PZEV emission standard.
The Cruze and Volt are both ULEV rated when running on their gasoline engines. The Jetta TDI is also ULEV rated. In other words equally clean whether gas or diesel.
Ford/Honda both claim they can make a SULEV or PZEV diesel easily; especially since the sulphur was removed from the fuel. And the start/stop is no big deal. The Lupo TDI had the technology back in 2002.
One of the main show stoppers for me is the fact that so far, with the exception of 2014 mazda6, diesel hybrids have exclusively been automatics. And as I have written before, I would rather walk or ride a bicycle than drive an automatic ever again.
If there were a diesel hybrid sportwagon with a manual transmission, it would be a viable alternative, at least to me.
With manual, you get to control the shifting point so the engine is always "singing" at the best rpm with most of the torque. With direct electric drives such as Volt, you get that max torque response at any rpm and any speed...
It has to be a manual in *everything*, not just in a hybrid. I will not pay for a vehicle with an automatic transmission - I suppose you can call it good old fashioned American "voting with my wallet", if I do not have any other say in the matter.
You might want to do it for fun. But it has nothing to do with the technology.
This is NO different from people who still "love" to ride horses, just b/c we have automobiles now...
I know. And I loathe the very thought of it. Driving will become horrible.
Try a Tesla S if you can...
Until I test-drove an EV.
Mind blown. It's so unbelievably responsive. Your right foot is like directly connected to the road. You get maximum torque/power all the time. Accelerations are uninterrupted. It's so fun to drive.
Now that was for a pure electric drivetrain, where the motor is permanently connected to the wheels (no clutch anywhere).
Serial hybrids should be just as good. Parallel hybrids have a lot more stuff in the way (planetary gears & co), and often smaller electrical motors, so your concerns would remain for those.
As for the article: Well that's nice opinion, but someone has BUILT a diesel hybrid car. They replaced their Honda Insight's gasser engine with a 1.2L diesel engine. It now gets over 90mpg on the highway (100+ with a skilled driver) and has great acceleration thanks to the electric motor assist.
Who here wouldn't want a 90mpg diesel hybrid car?
I think when you say "diesel hybrids have exclusively been automatic" you mean (non-hybrid) diesel cars? There aren't any diesel hybrids sold in the U.S. today, and I'm not aware that there will be for some time.
The 2014 Mazda6 is not a diesel *hybrid*, nor is the 2014 Mazda CX-5 that's expected to be the first Mazda to use the SkyActiv-D diesel engine.
When I talk about cars, I am almost never looking at just the North American market, and almost always looking at what is available elsewhere in the world, because my goal first and foremost is to have those same choices here in America.
The system charges capacitors during deceleration then uses that energy for the electrical system reducing the load on the engine for not having to run the alternator constantly from the engine.
The cost of diesel fuel is a big factor. For instance, the EPA estimates annual fuel cost for the Jetti TDI is virtually the same as an equivalent gasoline Focus. This situation is different in some countries in Europe where the cost of diesel is artifically supressed through taxation.
What we might see at some point is a move away from Atkins cycle to smaller GTDI (like the Jetta hybrid), or even Miller cyle with supercharger.
I agree with Xiaolong that diesel could be considered for a series hybrid (but a small GTDI might be cheaper/better).
Who here wouldn't want a 90mpg diesel hybrid car?
Also, in the US, diesel cost anywhere from 10%-15% more...(except when CA gas was $4.60/gallon and diesel was actually cheaper).
1. Package -- the tank takes up over half of the trunk in the Civic; batteries also are bulky; trying to fit everything in could be difficult.
2. Cost -- Like a diesel hybrid, you would be adding cost on top of cost and probably price it out of consideration for most buyers.
3. Infrastructure -- Still an issue on NG vehicles
4. Range -- Hybrid might help, but range is relatively short in Civic; tank holds the equivalent of about 8 gallons of gasoline.
And unlike the LNG tanks, LPG / propane tanks can now be extruded to effectively "flat " shapes rather than round cylinders, like has been done on the Holden (gm) commodore (again!) in Australia
There are 2 other issues that come to mind;
1. Keeping the fuel lines warm in winter. Diesel will gel in cold weather so you would have to heat the fuel line quite a bit anytime there is even a chance of needing the engine.
2. Fuel storage time. The Volt already burns through a tank per year whether you need it or not. I don't know if you would have to burn the diesel off more frequently. My guess is it is more stable, given that it is less volatile, but I am not a chemist.
You can, and it is. I had my diesel car sit for three years in storage with 75% of the tank, and when I cranked it, it fired right up.
The only concern is algae formation, but if one is careful to always pump at the same stations where the fuel storage tanks and the fuel is clean, even that is not an issue.
Changing the timing belt and the water pump is part of the standard maintenance procedure as documented by mazda, at every 60,000 miles (100,000 km), and it cost me the equivalent of $300 USD.
Rebuilding the engine costs far more, I know since I have done it myself multiple times, on several TOYOTA's no less.
I think that the above is called "FUD" - "Fear, Uncertainty, Doubt" in computer circles.
Any car can break. Why are diesel cars with particulate filters suddenly so different from gasoline ones with a catalytic converter?
I mean, really, seriously? Or is the whole goal of this website is to push electric and hybrid cars at all costs?
Just for the record, I stumbled upon this website looking for more inside news on diesel cars, not because I care about electrified cars and hybrids.
Mind blown. It's so unbelievably responsive. Your right foot is like directly connected to the road. You get maximum torque/power all the time. Accelerations are uninterrupted. It's so fun to drive."
I know they smoke tire, I know there is instant power on demand, but I cannot get past the fact that there is only the brake and throttle" pedal and nothing else. There is no clutch. No shifting. I cannot get past that.
And then I think about my baby - my clean diesel mazda6 parked in storage over in Europe, think about how I cannot import it here in the United States, and I feel the foam staring to form around my mouth...
Well, that is your problem. NOT an issue with the technology.
Riding horses are fun too, but I don't want them on my hwy either....
Out of the question!
Thanks for the info. It would seem that the billions(?) of miles covered by diesel/electric locomtives is solid evidence that such a system is an effective solution.
Well that's nice opinion, but someone has BUILT a diesel hybrid car. They replaced their Honda Insight's gasser engine with a 1.2L diesel engine. It now gets over 90mpg on the highway (100+ with a skilled driver) and has great acceleration thanks to the electric motor assist.
Who here wouldn't want a 90mpg diesel hybrid car?
.
Have an opinion?Join the conversation!