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Old 02-16-2012, 02:10 PM   #11 (permalink)
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Quote:
Originally Posted by Ryland View Post
you could just go with a single diesel engine and get great mileage while saving the weight of having a 2nd engine, after all diesels work best for highway cruising.
Yanmar makes some really nice 20hp and larger diesel engines that people have put in cars.
Reminds me of the guy that had the yanmar in his tracker? and is swapping it for a larger kubota and turbo.
If I wanted a non-towing/work diesel for high MPGs I would stick a turboed kubota in something small and RWD.

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Old 02-16-2012, 03:40 PM   #12 (permalink)
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As far as I can tell, pass. car gasoline engines have BSFC values that bottom out around 200-250 g/kw*hr. Doing the math on this on my factory engine (Saturn DOHC) running at peak efficiency @ 55mph came out to something crazy like 75mpg (EDIT: 8hp draw at 250g/kw*hr = 77mpg). A 120cc engine doing the same thing in my car would get the same mileage, only be MUCH MUCH easier to operate at peak efficiency.

Last edited by ProDarwin; 02-16-2012 at 03:50 PM..
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Old 02-16-2012, 04:10 PM   #13 (permalink)
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Quote:
Originally Posted by sheepdog 44 View Post
I haven't been doing any math, so help me figure out if the effort would be worth the possible gains in mpg and savings of this theory in a scientific way. What are the highway mpg improvements to be had by using a small displacement engine: less pumping and frictional losses, price, and better tuning for its purpose.

I want to find the hp required to cruise at 50mph and 65mph for a 95 civic dx/cv/vx. And cross reference it to the fuel consumption at that hp for the donor engine. It has to be cheap, and it doesn't matter where it comes from such as motorcycle, moped, light industrial etc as long as its fuel efficient. The optimal engine would be the Loremo 20hp turbo diesel but i couldn't find the specs for that engine.

Here are just the first examples i could find but I can't translate the fuel consumption of these engines from g/hph or litres a kilowatt hour.

20hp electric start small V-Twin Diesel engine 912cc products, buy 20hp electric start small V-Twin Diesel engine 912cc products from alibaba.com

20hp two-cylinder diesel engine products, buy 20hp two-cylinder diesel engine products from alibaba.com

Honda Engines - GX630 4-Stroke Engine
Hi sheepdog,
I've been thinking along the same lines for a long time. I've concluded that gasoline-electric hybrid, Prius style, gets the best results.
But anyway, if you go to this page on the ecomodder site and plug in the numbers for your car you see that the power to cruise is from 15 to 20 hp for 55 to 65 mph. But note the default weight is sub compact, the tire RR default is the best LRR tires you'll ever see, and the frontal area is quite small, but perhaps your car size.
So looking at the 3 engines you selected. I couldn't see any fuel use numbers for the Honda. The Haige is a diesel generator set so consider the efficiency of the generator, which itself might be between 50% and 80%, I don't know. Anyway they claim 280 g/kw hr. Diesel energy density works out to about 80g/kw hr so the overall efficiency of the genset is 80/280 or about 28%. The LAUNTOP diesel engine claims 200g/hp hr. continuous, which means at the 3000 rpm speed, 17 hp, Diesel energy density is about 60g/hp hr: 60/200 = 30% efficient. Now to cruise you'll need to vary the engine power and road speed over some range so you need a variable transmission of some kind and its losses. Take the 30% efficient engine, and assume 17 hp cruising at 60 mph. Again diesel has about 50 hp hr per gallon at 30% is 15 hp hr per gallon available. So 17 hp continuous needs just over (1.13) a gallon an hour or about 53 mpg.

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Old 07-30-2013, 08:24 PM   #14 (permalink)
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Quote:
Originally Posted by ProDarwin View Post
As far as I can tell, pass. car gasoline engines have BSFC values that bottom out around 200-250 g/kw*hr. Doing the math on this on my factory engine (Saturn DOHC) running at peak efficiency @ 55mph came out to something crazy like 75mpg (EDIT: 8hp draw at 250g/kw*hr = 77mpg). A 120cc engine doing the same thing in my car would get the same mileage, only be MUCH MUCH easier to operate at peak efficiency.
My 360cc 2 cycle motor has enough trouble getting a 900lb car to 55mph, a 125cc motor would likely net a top speed of 40mph assuming there are no hills
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Old 07-30-2013, 08:31 PM   #15 (permalink)
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Coupling thru a single gearbox would be the challenge, but could take a look at the viscous coupling setup from the early Greyhound's Scenicruiser buses which had a pair of Detroit Diesel 4-71 engines when the 8V-71 wasn't already available.
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Old 08-01-2013, 02:59 AM   #16 (permalink)
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Quote:
Originally Posted by sheepdog 44 View Post
I haven't been doing any math, so help me figure out if the effort would be worth the possible gains in mpg and savings of this theory in a scientific way. What are the highway mpg improvements to be had by using a small displacement engine: less pumping and frictional losses, price, and better tuning for its purpose.

I want to find the hp required to cruise at 50mph and 65mph for a 95 civic dx/cv/vx. And cross reference it to the fuel consumption at that hp for the donor engine. It has to be cheap, and it doesn't matter where it comes from such as motorcycle, moped, light industrial etc as long as its fuel efficient. The optimal engine would be the Loremo 20hp turbo diesel but i couldn't find the specs for that engine.

Here are just the first examples i could find but I can't translate the fuel consumption of these engines from g/hph or litres a kilowatt hour.

20hp Electric Start Small V-twin Diesel Engine 912cc - Buy Small V Twin Engine,20hp Diesel Engine,Electric Engine Product on Alibaba.com

20hp Two-cylinder Diesel Engine - Buy Two-cylinder 4-stroke Air-cooled Engine,Small Engine 20hp,Engines For Sale Product on Alibaba.com

Honda Engines - GX630 4-Stroke Engine
First lets figure out a good approximation for your HP needs to run a 1995 Civic at 50 and 65 mph.

In order to do this we need to get some data on the Civic.

#1. Coefficient of drag = .31 For hatch model link = Vehicle Coefficient of Drag List - EcoModder

#2. Frontal area = 19.9 same link as above

#3. Curb weight = 2094 lbs Civic VX Hatch Link = Honda Civic Compare - Exterior Features - MSN Autos

Now use this calculator and input data = Calculate HP For Speed

Your approximate horsepower requirements equals:

50mph = 8.89HP
65mph = 16.28HP

GH

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