# Diesel Engines
**URL:** https://boards.straightdope.com/t/diesel-engines/432236
**Category:** Factual Questions
**Created:** [January 4, 2008, 4:26am UTC](https://boards.straightdope.com/t/diesel-engines/432236 "2008-01-04T04:26:07Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@mks57](https://boards.straightdope.com/u/mks57)
#### Post date: [January 4, 2008, 4:26am UTC](https://boards.straightdope.com/t/diesel-engines/432236/1 "2008-01-04T04:26:07Z")
While reading some material on the history of internal-combustion engines, I began to wonder why diesel engines aren’t more common. What are the practical reasons that they aren’t in wider use? Is there a practical limit to how small they can be?
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### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [January 4, 2008, 4:31am UTC](https://boards.straightdope.com/t/diesel-engines/432236/2 "2008-01-04T04:31:12Z")
You mean other than diesels being noisy, smelly, and emitting copious quantities of particulate matter?
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### Author:  [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)
#### Post date: [January 4, 2008, 4:49am UTC](https://boards.straightdope.com/t/diesel-engines/432236/3 "2008-01-04T04:49:35Z")
Good question, but I think it’s more of a perception issue in the US.
In Europe diesels are pretty popular, I’m told because of the relatively good “gas” mileage and the long endurance of their engines. I own two hybrids and when I was in Germany last month they thought it was strange that anybody would buy a hybrid when diesels are cheaper and better (older technology). I don’t think any car company has been successful selling hybrids iagainst diesels n Europe.
Unfortunately for diesels, back in the 80’s the US car manufacturers made some pretty lousy ones and that really tarnished their reputations. I think VW and Mercedes are introducing new diesel models in the US over the next few years.
I have noticed that the cost of diesel fuel in California is more than for high octane gas… so it’s not going to save you much money there.
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### Author:  [@Merkwurdigliebe](https://boards.straightdope.com/u/Merkwurdigliebe)
#### Post date: [January 4, 2008, 5:03am UTC](https://boards.straightdope.com/t/diesel-engines/432236/4 "2008-01-04T05:03:41Z")
[QUOTE=Musicat]
You mean other than diesels being noisy, smelly, and emitting copious quantities of particulate matter?
[/QUOTE]
I drive a diesel and I take offense.
Opinions like yours are forged by idiotic policy in the US which led to the awful diesels by GMC in the 80’s.
Think about the early days. Do you really think that the early gasoline engines were any less noisy or smelly? Currently, auto diesels are very quiet, not smelly, and are very good in terms of particulate matter. Oh yeah, did I mention that I also get 45+ MPG? Jealous yet?
When it comes to Europeans not buying hybrids, why would they? Diesels get better MPG, and cost less. Secondly, how environmentally friendly are these hybrids that have gigantic batteries. What is the environmental cost of manufacturing those batteries?
I think the whole hybrid thing has come about because people are too stubborn to reevaluate their opinions of diesels.
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### Author:  [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)
#### Post date: [January 4, 2008, 5:46am UTC](https://boards.straightdope.com/t/diesel-engines/432236/5 "2008-01-04T05:46:47Z")
[QUOTE=mks57]
While reading some material on the history of internal-combustion engines, I began to wonder why diesel engines aren’t more common. What are the practical reasons that they aren’t in wider use? Is there a practical limit to how small they can be?
[/QUOTE]
Practical reasons they aren’t in wider use:
- Heavier
- More expensive (take the money you could save by buying gas instead of diesel and balance that against the cost of fuel)
- Less horsepower for their size and weight
Practical limit to how small they can be?
- Not in automotive terms, no. Recently, Volkswagen has sold a 1.9 liter diesel, which is about as small as the US market has any use for in a compct. I believe Ford was or is producing a 1.6 liter diesel for the Euro market.
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [January 4, 2008, 6:11am UTC](https://boards.straightdope.com/t/diesel-engines/432236/6 "2008-01-04T06:11:03Z")
[QUOTE=Musicat]
You mean other than diesels being noisy, smelly, and emitting copious quantities of particulate matter?
[/QUOTE]
You forgot to mention that they don’t like to start in the cold.
Actually, I’ve driven a friend’s VW diesel and really couldn’t even tell that it was a diesel. Diesels have come a long way since the klunkers of the 70’s and 80’s.
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [January 4, 2008, 6:28am UTC](https://boards.straightdope.com/t/diesel-engines/432236/7 "2008-01-04T06:28:37Z")
[QUOTE=Merkwurdigliebe]
Opinions like yours are forged by idiotic policy in the US which led to the awful diesels by GMC in the 80’s.
[/QUOTE]
Which idiotic government policy was it that cased GM to create those abortions? From everything I have read, those engines where the result of too many people at GM thinking their shit did not stink. No government stupidity needed, GM had plenty of of their own stupidity in stock.
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### Author:  [@kferr](https://boards.straightdope.com/u/kferr)
#### Post date: [January 4, 2008, 12:52pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/8 "2008-01-04T12:52:47Z")
On the question about diesel size limits - the VW Polo Blue Motion has a 3 cylinder 1.4 litre, can get 70mpg with lower CO2 emissions than a Prius. The Smart CDI has a 800cc 3 cylinder and gets 90mpg.
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### Author:  [@brewha](https://boards.straightdope.com/u/brewha)
#### Post date: [January 4, 2008, 1:34pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/9 "2008-01-04T13:34:27Z")
[QUOTE=mks57]
Is there a practical limit to how small they can be?
[/QUOTE]
The smallest diesel I’ve seen is less than 1cc displacement. .049 in^3
[PAW Diesel](http://www.eifflaender.com/enginepics.htm)
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### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [January 4, 2008, 1:51pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/10 "2008-01-04T13:51:17Z")
> [@](#):
>
> > [@](#):
> >
> > :
> > Originally Posted by Musicat
> > You mean other than diesels being noisy, smelly, and emitting copious quantities of particulate matter?
>
> I drive a diesel and I take offense.
I don’t think **musicat** ’s opinion derives from experience with US auto industry’s attempts at diesel. If mc’s experience is like mine, it derives from sharing the road with huge, odoferous, smoke-belching diesal trucks. They may say that these behemoths are clean-burning and efficient, but a lot of what I see on the road seems to defy that characterization.
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### Author:  [@Balthisar](https://boards.straightdope.com/u/Balthisar)
#### Post date: [January 4, 2008, 3:26pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/11 "2008-01-04T15:26:01Z")
Just for the record, European diesels were just as bad as American diesels back when the Americans were playing around with the idea. The difference is, the Europeans didn’t give up. Current European and American diesels are still relatively dirty. Newer generations of American diesels will be vastly cleaner than European diesels, though.
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### Author:  [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)
#### Post date: [January 4, 2008, 3:33pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/12 "2008-01-04T15:33:07Z")
[QUOTE=mks57]
While reading some material on the history of internal-combustion engines, I began to wonder why diesel engines aren’t more common. What are the practical reasons that they aren’t in wider use? Is there a practical limit to how small they can be?
[/QUOTE]
Umm…50% of all cars sold in Europe are oil burners.
[Cite from CNN](http://money.cnn.com/2007/05/01/autos/diesels/index.htm)
67% of all BMWs sold in Europe are diesels.
[Cite.](http://www.nytimes.com/2006/12/17/automobiles/autoreviews/17BLOCK.html?fta=y)
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### Author:  [@Philster](https://boards.straightdope.com/u/Philster)
#### Post date: [January 4, 2008, 3:35pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/13 "2008-01-04T15:35:16Z")
There are more diesels in the US than you think. Trucking is a powerhouse in the United States, and the industry is fueled by Diesel. You can’t go very far in the US without encountering diesel after diesel engine.
Big open roads and a fascination with the driving characteristics of the gas engine through circa 1972 met face-to-face with pollution control laws and other federal mandates that forced American car makers to focus on what they knew: gasoline power. Once they got caught up in the chase to make the gas engines work better, and make them efficient and clean, they simply did not have the ability to become a diesel industry.
Foreign makes with diesel power saw little success. The American consumer was used to the characteristics of gasoline engines and was not creating the demand for the potential supply from overseas.
The trucking industry, in **dire** need of raw low-end torque and climbing power – especially as gas-powered engines saw their horsepower plummet through the 70s/80s – created a **huge** demand for diesel engines, and the US diesel trucking industry alone might rival other countries diesel car industry.
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### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [January 4, 2008, 4:47pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/14 "2008-01-04T16:47:47Z")
[QUOTE=Merkwurdigliebe]
I drive a diesel and I take offense.
[/quote]
I didn’t mean _your_ diesel, which I’m sure smells like lilacs in May. 🙂
Maybe things have changed. Are trucks and busses no longer belching smoke and smells? Can you now stand next to a bus at a stop and not get bowled over, smell-wise, when it drives away? That was always my experience.
My only experience with passenger-sized diesels is a station wagon owned by a friend in the 1970’s. She used it primarily to ferry stray dogs to/from the shelter, and bought that car to save on fuel costs. No matter where you stood or sat in or around that car, during idling or highway driving, the smell was there. It overwhelmed the dog smell by a nose.
When I asked her if it was running OK or if it needed mechanical work, she said she always kept it in good shape and her mechanic said there was nothing wrong with it.
Other than that anecdote, I have nothing else to add.
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### Author:  [@Tully\_Mars](https://boards.straightdope.com/u/Tully_Mars)
#### Post date: [January 4, 2008, 5:53pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/15 "2008-01-04T17:53:13Z")
Diesel engines are mathematically more efficient than gasoline engines because they are able to operate at a higher combustion ratio. The combustion is also more complete, resulting in less carbon monoxide and (I think) less carbon dioxide.
However, the higher combustion ratio means higher cylinder pressures. These means higher forces acting on the valves, the pistons, the crankshaft, and the bearings. This means the cyclic loading/unloading on those parts is greater, which causes them to to fatigue sooner. To remedy this, all of these parts in a diesel engine must be heavier than the comparable part in a gas engine.
If you’re designing an engine for a Peterbilt, that’s not a problem. GM, in their rush to get a product to market in the '70s, chose to ignore these details and as a result created an public perception that diesels were not suited for automobiles.
All of this additional mass means that the rotational inertia of the diesel engine is greater than that of a comparable gas engine. That means it doesn’t like to change RPMs very much. This means a diesel powered car will not zip around the boulevard with the same throttle response as a BMW without some sort of transmission compensation. Again, if you’re designing a Peterbilt, that’s not a problem.
The good news is that advances in material science, computer aided design, and computer engine control systems are beginning to reduce the amount of metal mass needed to support the pressures of the diesel engine cycle. My perception is that Volkswagen and Mercedes are the leaders in this effort.
I saw an article in Cycle World a couple of months ago where Neander has prototyped a two-cylinder diesel motorcycle. The torque numbers were awesome. They are using a dual-shaft, counter-rotating crank to control vibration. It looked promising.
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### Author:  [@Throatwarbler\_Mangrove](https://boards.straightdope.com/u/Throatwarbler_Mangrove)
#### Post date: [January 4, 2008, 6:11pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/16 "2008-01-04T18:11:36Z")
I think you mean _compression ratio_.
The big advance with car diesels is turbocharging. Diesel engines already operate at high compression ratios and don’t need extra reinforcement to handle forced induction. The cooler exhaust gas and narrower operating range means less stress on the turbocharger and less compromising performance, and because diesel engines use direct injection, it is less sensitive to knock than a gasoline engine (I’m not 100% certain on the technical details of the last bit, maybe someone else can explain it).
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### Author:  [@Great\_Dave](https://boards.straightdope.com/u/Great_Dave)
#### Post date: [January 4, 2008, 6:19pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/17 "2008-01-04T18:19:03Z")
Test drive a VW Golf TDI. If you haven’t seen a diesel car in a while, you will be impressed- fairly quiet, low odor, starts in the cold pretty easily- just wait a moment for the glow plugs, and it will get up and go when the hammer is down.
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### Author:  [@Tully\_Mars](https://boards.straightdope.com/u/Tully_Mars)
#### Post date: [January 4, 2008, 6:21pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/18 "2008-01-04T18:21:06Z")
[QUOTE=Throatwarbler Mangrove]
I think you mean _compression ratio_.
[/QUOTE]
Oops. Thanks.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [January 4, 2008, 6:35pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/19 "2008-01-04T18:35:10Z")
I remember Diesel cars being readily available in California, especially after the second Oil Embargo. But when I checked Diesel VW Golfs a few years ago, I found they weren’t available there. It seems that the fuel efficiency of Diesel cars was trumped by California’s strict anti-pollution laws. But I recall a couple of years ago that Diesels were being sold again in California.
Diesel engines are now flying in some 1,500 aircraft worldwide. That number is expected to rise by 500 by the end of the year.
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### Author:  [@633squadron](https://boards.straightdope.com/u/633squadron)
#### Post date: [January 4, 2008, 7:23pm UTC](https://boards.straightdope.com/t/diesel-engines/432236/20 "2008-01-04T19:23:43Z")
[QUOTE=mks57]
While reading some material on the history of internal-combustion engines, I began to wonder why diesel engines aren’t more common. What are the practical reasons that they aren’t in wider use? Is there a practical limit to how small they can be?
[/QUOTE]
Your perception is based on the prevalence of gasoline engines in _US cars_.
For wheeled vehicles, gasoline engines probably outnumber diesels. There are no production diesel motorcycles, and lots of gasoline motorcycles, cars, and light trucks.
Gasoline engines also prevail in internal-combustion aircraft (for the moment).
Gasoline engines also prevail in sport marine and most sailboat auxiliaries.
On the other hand, semi-trailer vehicles are almost exclusively diesel. Commercial marine and navy internal-combustion is diesel. Railroad internal-combustion is exclusively diesel.
Diesel is particularly suited to large-scale engines that need to produce significant power and torque at low output shaft speed. A race car doesn’t get any benefit from diesel, but a pickup truck that can pull stumps does.
Railroad “diesel” locomotives are actually diesel-electrics: the diesel engine powers an electric generator which then feeds current to motors at each drive wheel. The generators don’t run at high speed but their torque requirements are enormous. Of course, electricity is used because you can turn an electric motor under load.
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