# How efficient is a diesel engine vs...?



## seedspreader (Oct 18, 2004)

This is a hard question that no one may know the answer to, but here goes.

I've read that diesel's are 20% more efficient that gasoline engines, meaning they extract more of the store energy than gas. 

First of, I don't know if that's true or not, and it could just be erroneous... BUT, I am fairly confident that an Electric Engine (motor/whatever you call it) is the most efficient use of energy in vs. the return on energy out.

I know that hybrids work on the theory that those efficiencies happen at different torque/RPM ranges, etc.

What I am trying to figure out here... and stick with me, because I know it's convoluted... But...

I see these little diesel generators (say one that has a perkins engine and are rated at 1800 rpm vs. the 3600 rpm cheapies) that say they can run 8 hours on 3 gallons, etc.

Would you be better off (if you were building a vehicle) to use the diesel engine direct for powering a vehicle, or would you be better off running a battery system/electric engine (knowing that you will lose a certain efficiency from the diesel to electric conversion)?

I guess my thoughts are that at low RPM you would be pulling more amps off stored power in the batteries and the diesel at higher rpms of the electrical engine is not having the same draw (since it takes less energy to maintain speed on a flat plain than it does to start something moving).

Or are you always going to get the best efficiency just using the diesel straight off? 

I KNOW the best system is a hybrid, but that takes quite a bit of engineering for a home tinkerer.


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## michiganfarmer (Oct 15, 2005)

All I know is the fuel consumtion I have seen. My dads 1999 ford with a 7.3 liter diesel can pull his 14,000lb 5th wheel camper, and get 14 mpg. Anyone i know with the ford 460 gas engine, wich is about 7.5 liter, gets 9 mpg pulling nothing, and worse when its working.

My 2 cylinder 60 horse power john deere can work all day under full load, and only use 12 gallons of fuel, but my neighbors 50 horse gas 2 cylinder will use 20 gallons in a day.


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## Ross (May 9, 2002)

> Or are you always going to get the best efficiency just using the diesel straight off?


 The concept is sound enough you run your engine at a constant and store the waste energy when your stopped or slowing and release it when you accelerate or go above the point of generator production. Something like a locomotive or submarine. The issue is weight, availability of components and operating times. New batteries would probably get it scaled down to truck size and there's new automotive electrics all the time. I don't know if you can get past the operating times. Trains and ships run 24/7 when their working, so you can size the diesel and genny to suit that. And it's efficient too. Not too big not too small. Cars are used for stop and start driving and mostly short term runs. You need a bigger than optimum engine/generator to stay ahead of the demands traffic imposes for leaving intersections or passing etc. or a way to store power from a smaller generator. Where it's a steady predictable load you can size a diesel electric system to run efficiently........... but maybe that could be done for a large truck now! The battery is the steady load (weight issue solved) there's new components availalbe (or could be) and if you can wrap your mind around the diesel genny running when the vehicle isn't moving to recharge the load (batteries)........... it might just work. Truckers run little diesel chillers 24/7 for cargo why not for the whole truck? Maybe it could be done for passenger vehicles too! Haven't thought about it in a long time.


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## WisJim (Jan 14, 2004)

You lose some efficiency, much of it as heat, every step of the way. Lose 10% (just as a guesstimate for illustration purposes) in the generator, 10% in using the batteries, 10% in electric motor losses. So you are losing nearly 30% just changing mechanical energy to electrical, storing it, and using it again, compared to using the mechanical power(diesel engine) to run the vehicle directly. 

Where you make up for some of these inefficiencies is by running the generator/engine only at its most efficient speed, so you minimize losses in power and reduce emissions. There are some good websites going into detail on the efficiencies of hybrids vs electric vs gas/deisel. http://www.ecoworld.com/Home/articles2.cfm?TID=373 isn't the best but has some useful information and illustrations. I can't seem to find the link I prefer.


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## Ross (May 9, 2002)

Oh yeah Mchiganfarmer is correct a diesel tractor will turn alot moe sod on a gallon of diesel than a gas tractor will on gasoline. I have a little 40 hp gas Ford tractor it eats more fuel spnning an auger than it's big brother (72hp) does pulling a set of discs through clay.


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## wy_white_wolf (Oct 14, 2004)

While WisJim is right about losing some everytime you convert energy that doesn't take in account that ICE work best at one particuler steady RPM. Just like noted that a vechile will do better at a steady state then accelerating and decelerating all the time. This is why the hybrids work. They even out the accelerations and declerations and allow the ICE to run steady state and shut down completely when not needed. With the right engineering an electric/desiel hybrid will do better than a straight desiel. 

But like seedspreader mentioned, not really a thing for shade tree mechanics or ******* engineering. If you don't get the balance right between the ICE and electric motor you will either waste all benifits in fuel wasted (to large a genset) or not be able to keep power in the batteries (to small a genset).


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## OntarioMan (Feb 11, 2007)

I'm guessing that cost and complexity are directly proportional to the efficiency in a hybrid vehicle. With enough money and enough engineering, you could probably produce vehicles which are far more efficient than anything out there today - but who could afford them?

Carbon fibre is twice the strength of steel and half the weight of aluminum - but you don't see consumer vehicles made of carbon fibre. One of the drawbacks to electric vehicles is the cost of all the electric components. 

If tinkering with a more "fuel efficient" cheap vehicle is your goal - perhaps something lightweight with a tiny fuel powered engine in it. A U.S. university stuck a Kubota 3 cylinder diesel in a Metro and hit almost 100 mpg on a test track. At one time, the Suzuki "carry all" truck available in Japan had a 3 cylinder 660cc engine. Propane and natural gas may be fuel options as well. 

Perhaps its just me, but it appears that North Americans drive commuter vehicles which are way overpowered. My old Mazda 323 is a 1600cc, and in the city, it is way overpowered. Would I trade some of that power for more fuel efficiency, you bet!

.


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## Explorer (Dec 2, 2003)

Don't railroad locomotives use a diesel genset to power their electric drive motors?


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## SolarGary (Sep 8, 2005)

Hi,
The new Chevy Volt works pretty much as you describe, but uses a gas engine, not a diesel.
The Volt is basically an electric car with the batteries charged by an IC engine running at its most efficient area. The IC engine is not connected to the drive train at all.

It looks like GM is putting a lot of effort into this area:
http://gm-volt.com/

--- 
One thing to bear in mind when comparing diesel efficiency to a regular IC is that diesel fuel has more energy per gallon -- so part of the diesel gain is due to the higher efficiency of the diesel cylce, but part is just due to diesel fuel having more energy per gallon.

Gary


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## Michael Kawalek (Jun 21, 2007)

HI Seedspreader
Diesel engines are more efficient for two reasons. First of all, because the pistons have a higher compression ratio (that is the air and fuel are squeezed into a smaller space they are thermodynamicly more efficient. Secondly, a gallon of diesel fuel is heavier than gasoline (6lbs/gal vs 5lbs/gal) so it has a greater amount of chemical energy that can be converted into power. Overall, I don't think it is a 20% improvement, I think it is more like 50+%. I have a Ford F350 with the diesel engine and I routinely get 20-21 mpg! Others with the same configuration in gasoline are getting 9-10 mpg!

You're right in the sense that a diesel engine would make a more efficient hybrid than a gasoline engine. In fact, VW is about to unveil a new diesel-hybrid Jetta next year. VW is claiming that it will get 69 MPG!

WisJim is correct that there are energy losses converting the engine power into electricity, and another loss when it comes back out of the battery. However, that loss is less than the loss you get sitting there idling at a red light. Stop and go traffic is a killer to good gas milage, but with a hybrid you're still storing power even while you're sitting there waiting.

Things change however once you're out on the open road. If you drove off on a straight cross-country highway trip without any stops, the regular ICE engine would win. That's because all the power goes straight to the wheels without any electric-motor/battery middlemen. That's why hybrids typically get lower mileage on the highway than in city driving. You have to decide what kind of driving most matches your personal habits. If you need a car for mostly stop and go city traffic, get the hybrid. If you need a car for long distance highway driving the straight diesel is your very best bet!
Michael


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## artificer (Feb 26, 2007)

Take a look at the XR3 

With just a 24hp Kubota diesel engine, it is supposed to get 125mpg. 2 person, little storage space, but only around 950 pounds.

You can build it 3 ways. Diesel, electric, hybrid. Its a parallel hybrid system, however.

To maximize efficiency, you want to run the engine as close to 100% max power for that rpm. In farming they say "Gear up/speed down" for field work. You want to keep you rpm's as low as you can, but still have enough power to drive/plow/whatever. This is one reason people are interested in CVTs. (continuously variable transmissions) These are the belt driven units on snowmobiles. The only downsides are belt life and inefficiencies during cruising. More cars are coming out with them. They have been around for a long time.

My take on why hybrid systems work so well are as follows:
Smaller engine needed. Your engine is operated closer to the 100% max power mark, more often. The extra boost is provided by the electric motor. You get the mileage of an small underpowered dog of a car, but have the acceleration of what we consider "normal cars".

Regenerative braking. Whenever you brake, you've just wasted all of that fuel needed to get you to that speed. Instead of brakes, you use your electric motor to slow you down, and put a charge back on the batteries. This is most useful in city driving.

Turn off the engine. If your doing stop and go driving, your power requirements are low. Just use the electric motor. Also, if you're idling at the stop light for a long time, kill the engine. You can get started on the electric motor, and the engine will kick in to keep you going.

From the top of my head, I remember gas engines as only being 20% efficient, and diesels being 35%.

Michael


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## Jim-mi (May 15, 2002)

The combo I'd like to see would be a 10hp Yanmar diesel charging the batterys of the hybrid.
With the diesel running at a easy going 15-1800 rpm.
You would get a whole lot of charging for a gallon of fuel .........
There would be no comparison between the diesel verses gas at that small of hp.


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## Auric (Jul 18, 2005)

Michael Kawalek said:


> Diesel engines are more efficient for two reasons. First of all, because the pistons have a higher compression ratio (that is the air and fuel are squeezed into a smaller space they are thermodynamicly more efficient. Secondly, a gallon of diesel fuel is heavier than gasoline (6lbs/gal vs 5lbs/gal) so it has a greater amount of chemical energy that can be converted into power.


There is a third way that diesels can be more miserly than their gas brethern. The VW TDI engine takes advantage of an ability to shut down the engine when coasting. If you aren't pressing down on the accelerator and the vehicle's speed is driving the engine, the computer quits injecting diesel into the cylinders. This cannot be done with a gas engine. This knowledge has caused me to wonder why a diesel engine wasn't already married to an electric motor in a hybrid...


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## Jim-mi (May 15, 2002)

I think the answer to that is in the gosh awful stingent rules and regs this country has placed on diesels.
I understand that Europe has more small diesel powered cars than gasoline powered.

Stay tuned . . .VW has a new diesel offering coming soon.


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## SolarGary (Sep 8, 2005)

Auric said:


> There is a third way that diesels can be more miserly than their gas brethern. The VW TDI engine takes advantage of an ability to shut down the engine when coasting. If you aren't pressing down on the accelerator and the vehicle's speed is driving the engine, the computer quits injecting diesel into the cylinders. This cannot be done with a gas engine. This knowledge has caused me to wonder why a diesel engine wasn't already married to an electric motor in a hybrid...


Some of the gas engine cars have a feature that deactivates some cylinders when the engine load is low. I guess this would accomplish the same thing.

http://www.worldcarfans.com/2060518.003/gm-39l-v6-gets-e85-ethanol-and-cylinder-deactivation
http://en.wikipedia.org/wiki/Cylinder_deactivation

The explanation I've heard for no diesel hybrids yet is that the extra expense of the hybrid electric drive features plus the extra expense of the diesel makes the total package very pricey.



Gary


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## tamsam (May 12, 2006)

For starters how good are the batteries that are out there? When you talk to a sales person about a hybrid and ask about battery life and the cost to replace them they get nervous and try to talk about everything else. I have had a few ideas about electric cars but have never been in a position to build one. I don't know why an engine couldn't be used to run a charging system to power a car. Sam


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## Michael Kawalek (Jun 21, 2007)

That is one of my questions also. I think that hybrid owners are going to receive a big shock when it comes time to swap out the batteries. I use a lot of recharges of all kinds, flashlights, phones, portable power supplies, and I'm the type that is devoted to proper charging procedures, and I still find all my batteries dying on me. I would never, ever buy a USED hybrid. Even with the best electronic management, batteries always deteriorate.


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## seedspreader (Oct 18, 2004)

How timely: http://money.cnn.com/2008/04/29/autos/gas_engine_improvements/index.htm?postversion=2008050216


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## vallyfarm (Oct 24, 2006)

They are about 30% more efficent than a gas engine comparing the same engine in both forms. EU has much higher standerds for fuel than we do. They also use emmisions over distance unlike us. We (USA) snif a tailpipe and find gas to be much cleaner than deisel, but deisel uses 30% less fuel, so over the course of a mile, for example, the deisel is actually a cleaner engine. This is with ULSD. That old crap is why many deisels aren't here. European engines won't even run too well on that crap. The new VW deisel engine is suppposed to be amaizing. To the point that the US delayed it being allowed in thes country because it would be unfair competition to the US auto industry. Really!! And unlike ethanol, bio-deisel runs even better. Cleaner, more power, longer engine life, Once cold weather gelling is cured, it'll be something. Also need to get those stupid soybean pushers out of bio-deisel. Soy is about the WORST thing to use. Far cheaper to grow and harvest and needs very little fert/pest/weed control is rape seed (canola in this country) It also gives 10x's more fule per acre. Thats right, 10x's more. The byproduct is also an excelent feed stock. Mike


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## Michael Kawalek (Jun 21, 2007)

Rapeseed is the ideal oil crop to plant in northern regions too cold for corn or soybeans. It's big in Canada, and yes the yield is high. A lot of crops produce much more oil than soybeans; sunflowers, oil palm in the tropics, and even olives.

Soybeans do have some critical advantages though. Because it's a nitrogen fixer, it creates its own nitrogen fertilizer. The pressed meal can also find a ready market for human food (tofu), animal feed, and even the plastics industry. And, it's a crop American farmers already know how to grow and have the machinery to harvest. What oil crop American farmers finally grow will probably have more to do with the local climate than anything else.

I'm still betting my money on bio-diesel. Its energy yield per acre is three times higher than ethanol, and it's a fuel that hobbyists can make in their own garages. Even though diesel is now more expensive than gasoline, its cost per mile is still lower. I am just biting at the bit to finally get a diesel powered car here in California.
Michael


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## SolarGary (Sep 8, 2005)

tamsam said:


> For starters how good are the batteries that are out there? When you talk to a sales person about a hybrid and ask about battery life and the cost to replace them they get nervous and try to talk about everything else. I have had a few ideas about electric cars but have never been in a position to build one. I don't know why an engine couldn't be used to run a charging system to power a car. Sam


Hi,

This is a quote from the Toyota website:

How long does the Prius battery last and what is the replacement cost?

"The Prius battery (and the battery-power management system) has been designed to maximize battery life. In part this is done by keeping the battery at an optimum charge level - never fully draining it and never fully recharging it. As a result, the Prius battery leads a pretty easy life. We have lab data showing the equivalent of 180,000 miles with no deterioration and expect it to last the life of the vehicle. We also expect battery technology to continue to improve: the second-generation model battery is 15% smaller, 25% lighter, and has 35% more specific power than the first. This is true of price as well. Between the 2003 and 2004 models, service battery costs came down 36% and we expect them to continue to drop so that by the time replacements may be needed it won't be a much of an issue. Since the car went on sale in 2000, Toyota has not replaced a single battery for wear and tear."


Gary


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## mightybooboo (Feb 10, 2004)

SolarGary said:


> Hi,
> 
> This is a quote from the Toyota website:
> 
> ...


And since Chevron (with their subsidiary Cobasys) now controls the rights to the EV-95 NiMh battery that got 100-150 miles per charge,cars will only get 40 miles per charge.Because thats the largest battery they will allow to be built in NiMh.

NiMh in the Rav4 Electric got 100 miles minimum and 150 mile maximum range,and at freeway speeds in a real sized car,with airconditioning!

At 100-150,000 mile durabilty tests (real road miles) SCE found about 10% degradation,not counting one vehicle that had a bad battery from the get gwners report virtually no loss in battery depth.

I'd say thats a darn good battery,the EV-95.Too bad Chevron was able to bury it and refuses to license its production.

SCE also figured mass produced it should cost 1000-2000 per battery pack.Small wonder Chevron buried it,it was a viable threat to the ICE engine.And being very reliable with few moving parts GM sure as heck didnt want it (electric cars) marketed either.But not to worry,GM will make sure the Volt is a mechanical nightmare like their current vehicles.

Soooo....until Li-Ion can deliver what the EV-95 did ten years ago you will have maximum 40 mile electric cars.Should keep viable electrics off the roads for many many more years,much to GM and Chevrons delight.

Oh,and Cobasys now has its tentacles firmly around A123 systems,so look for Li-Ion if it ever reaches its potential to be strangled by Chevrons baby Cobasys and its control at A123 systems.Nice to see the Oil companies firmly in control of electric car batteries.


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## mightybooboo (Feb 10, 2004)

http://pppad.blogspot.com/2007/05/nimh-held-hostage-by-chevron-texaco.html

Toyota, working to meet the Zero Emission Vehicle mandate, set up a production line in 1997 for the "large-format" EV-95 batteries needed for their Toyota RAV4-EV.

These EV-95 NiMH batteries, after years of research, were perfected for EVs:

* Deep Cycle, no memory effect;

* High energy output for acceleration;

* Long lifetime, longer than the life of the car -- even a Toyota car. Toyota's EV-95 batteries are still running Toyota RAV4-EV cars more than 20,000 miles per year, and for over 100,000 miles so far.

But no more EV-95 batteries can be made, after Chevron sued Toyota.


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