Diesel engine efficiency
- Thread starter Tourist
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Totatl engine efficiency or combustion efficiency? Ball park figures for a modern engine I would guess a gas engine to be about 55% and a diesel about 75-80%. I'm really just taking a shot in the dark on that one.
The combustion efficiency with modern engines is quite a bit higher. Probably 90%+, but overall efficiency will not nearly that high. Frictional losses have to be accounted for and the biggest loss is heat energy. Instead of electric hybrid drives I think a better solution are steam hybrid drives. Use the waste heat energy to heat water in a very high efficiency boiler and incorporate a steam motor into a traditional automatic transmission.
The combustion efficiency with modern engines is quite a bit higher. Probably 90%+, but overall efficiency will not nearly that high. Frictional losses have to be accounted for and the biggest loss is heat energy. Instead of electric hybrid drives I think a better solution are steam hybrid drives. Use the waste heat energy to heat water in a very high efficiency boiler and incorporate a steam motor into a traditional automatic transmission.
If I had to guess, I'd guess lower than that.
Most of the waste heat is at too low a temperature to be very valuable as an energy source for steam production. BMW's system only increases efficiency by about 15%, but that may be enough to be useful in production vehicles at some point.
JHZR2
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The high efficiency EDGs for ships are about 37% efficient, this is for big 18-cylinder 500kWe units.
I doubt that one will do a lot better than that LHV in to power at the wheels out, for a diesel... probably 32-35% is right... Gassers are probably right at 15-20% like said above, but Id venture to guess that some of the better units push 25%.
JMH
I doubt that one will do a lot better than that LHV in to power at the wheels out, for a diesel... probably 32-35% is right... Gassers are probably right at 15-20% like said above, but Id venture to guess that some of the better units push 25%.
JMH
The little diesel in the VW Lupo has a 44% point in its operating range, which is pretty good for such a small engine.
The difference between a gasoline and diesel engine both producing the same power output is 20-25%.An excellent way to compare is the difference between a gasoline and diesel powered boat at the same cruising speed. The absolute thermal efficiency of a gasoline engine is very approximately 12-25%. A lot depends on compression, engine speed, and the gasoline used.
Also, take this into consideration... Energy per gallon of fuel.
1 Gallon Gasoline = 125,000 BTU
1 Gallon Diesel = 147,000 BTU
Just right there you've got yourself another 17% in energy per gallon of fuel you've purchased. Then apply the other efficiencies of the diesel engine and you have a win win situation.
1 Gallon Gasoline = 125,000 BTU
1 Gallon Diesel = 147,000 BTU
Just right there you've got yourself another 17% in energy per gallon of fuel you've purchased. Then apply the other efficiencies of the diesel engine and you have a win win situation.
Dominic,
Believe I read in Road & Track that a gallon of ethanol has 78% the energy of a gallon of gas. If measured in BTUs that would be about 97,500. State law here in Hawaii mandates 10% ethanol in our gas, so I guess a typical gallon of gas/ethanol has 122,250 BTUs. All the more reason to prefer diesel.
Can you tell me whether octane and cetane ratings affect the energy in BTUs of gasoline and diesel fuels?
Thanks,
Mark
Believe I read in Road & Track that a gallon of ethanol has 78% the energy of a gallon of gas. If measured in BTUs that would be about 97,500. State law here in Hawaii mandates 10% ethanol in our gas, so I guess a typical gallon of gas/ethanol has 122,250 BTUs. All the more reason to prefer diesel.
Can you tell me whether octane and cetane ratings affect the energy in BTUs of gasoline and diesel fuels?
Thanks,
Mark
Cetane levels are the inverse of octane levels.
The way to think about it is as follows:
More Cetane = More Volatile = Easier to go boom
More Octane = Less Volatile = Harder to go boom
Also, Diesel fuel has an octane level of 25 - but this is ok since diesel engines are of course compression engines and need that rampid combustibility that gasoline doesn't need (thanks to spark plugs). Luckily, its heavier weight, so it burns slower once it combusts, and hence the cool engine sounds.
Your statement is correct about the lower energy levels of gasoline when combined with EtOH. However, the EtOH is used to raise the "octane" level of the gasoline to keep it from preigniting. The funny thing is, not all octane boosters lower the BTU level of gasoline - MTBE and lead keep the energy levels the same or raise them, but there goes the environment right?
Also, this means that running E10 Gas which has 2-3% less energy means your economy will also drop by 2-3% no matter what you do. That turns a 30mpg car into a 29mpg car, and from what I've discovered its really more like a 5% loss in economy. Since the nation switched to E10 my highway (and friends) has dropped by 3-5% city and highway.
I want a diesel. My dad has a 06 TDI and hasn't got less than 43mpg with it, with a max of around 48mpg.
The way to think about it is as follows:
More Cetane = More Volatile = Easier to go boom
More Octane = Less Volatile = Harder to go boom
Also, Diesel fuel has an octane level of 25 - but this is ok since diesel engines are of course compression engines and need that rampid combustibility that gasoline doesn't need (thanks to spark plugs). Luckily, its heavier weight, so it burns slower once it combusts, and hence the cool engine sounds.
Your statement is correct about the lower energy levels of gasoline when combined with EtOH. However, the EtOH is used to raise the "octane" level of the gasoline to keep it from preigniting. The funny thing is, not all octane boosters lower the BTU level of gasoline - MTBE and lead keep the energy levels the same or raise them, but there goes the environment right?
Also, this means that running E10 Gas which has 2-3% less energy means your economy will also drop by 2-3% no matter what you do. That turns a 30mpg car into a 29mpg car, and from what I've discovered its really more like a 5% loss in economy. Since the nation switched to E10 my highway (and friends) has dropped by 3-5% city and highway.
I want a diesel. My dad has a 06 TDI and hasn't got less than 43mpg with it, with a max of around 48mpg.
Gasoline engines vary in thermal efficiency depending on load. At light loads (eg cruising conditions) they are REALLY BAD! Typically 5-10% thermal efficiency when outputing 20hp. At full throttle with lowish RPMs, eg 2500 or so they reach 25% efficiency.
Diesels fair a little better on the partial load efficiency because the air supply is not throttled. However they're still not great. Best diesel efficiency is probably somewhere in the 30's. The very best ever recorded is 56%.. that's the current record.. for a huge engine running something like 200rpm..
Diesels fair a little better on the partial load efficiency because the air supply is not throttled. However they're still not great. Best diesel efficiency is probably somewhere in the 30's. The very best ever recorded is 56%.. that's the current record.. for a huge engine running something like 200rpm..
I have a book about the Nebraska Tractor Tests since 1920. There were over 1500 individual tactors tested for various performance criterion, incuding fuel consumption. Several fuels were used; diesel, gasoline, kerosene, propane, distillate, and an obscure fuel called "tractor fuel" which was somewhere between kerosene and gasoline.
They measured fuel consumption in Horsepower Hours per Gallon of fuel rather than the more scientifically correct Pounds of Fuel per Hour. Most farmers have a better conception of Gallons rather than Pounds of fuel, and fuel is indeed normally sold by the gallon.
From 1920 to 1984 fuel consumption was all over the map, from pretty good to plumb awful.
Diesels went from a low of 9.29 HP-HRS/Gal to a high of 18.64 HP-HRS/Gal. The mighty John Deere 720 Diesel (naturally aspirated) set a record of 17.97 in 1956, which stood until 1983 when a Japanese-built, turbocharged John Deere Model 1650 finally beat it.
The gasoline engines went from an abysmal 3.30 HP-HRS/gal (a little single cylinder flathead model) to a high of 13.18 HP-HRS/gal in 1960 by the Oliver Model 1800.
No propane tractor exceeded 9.99 HP-HRS/gal, achieved by the Case Model 910-B in 1959. The lowest propane economy was 7.26 in a Ford Model 640-L.
The gasoline engines typically showed the best fuel economy at Full Power Rating, the diesels tended to drop off just a bit at max power. The old Distillate engines did rather well with a best rating of 12.44 HP-HRS/gal by a Farmall M in 1939. That engine used a compression ratio of less than 5:1 folks. Not bad for ancient technology.
Joe
They measured fuel consumption in Horsepower Hours per Gallon of fuel rather than the more scientifically correct Pounds of Fuel per Hour. Most farmers have a better conception of Gallons rather than Pounds of fuel, and fuel is indeed normally sold by the gallon.
From 1920 to 1984 fuel consumption was all over the map, from pretty good to plumb awful.
Diesels went from a low of 9.29 HP-HRS/Gal to a high of 18.64 HP-HRS/Gal. The mighty John Deere 720 Diesel (naturally aspirated) set a record of 17.97 in 1956, which stood until 1983 when a Japanese-built, turbocharged John Deere Model 1650 finally beat it.
The gasoline engines went from an abysmal 3.30 HP-HRS/gal (a little single cylinder flathead model) to a high of 13.18 HP-HRS/gal in 1960 by the Oliver Model 1800.
No propane tractor exceeded 9.99 HP-HRS/gal, achieved by the Case Model 910-B in 1959. The lowest propane economy was 7.26 in a Ford Model 640-L.
The gasoline engines typically showed the best fuel economy at Full Power Rating, the diesels tended to drop off just a bit at max power. The old Distillate engines did rather well with a best rating of 12.44 HP-HRS/gal by a Farmall M in 1939. That engine used a compression ratio of less than 5:1 folks. Not bad for ancient technology.
Joe
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