Sub 20 HP air cooled gasoline engine fuel efficiency vs sub 30 HP liquid cooled diesel.

[etpm]

The subject is my question. How would a 14 HP air cooled gasoline engine compare to an approx. 27 HP liquid cooled diesel engine. I know that on an equal type basis the gas engine is going to use about 20% more fuel than the diesel when powering the same load. But this is not an equal comparison. The gas engine is an overhead valve air cooled generic engine in a Generac generator. I said generic because I'm thinking that all the engines made for this type of work are pretty much the same. Especially since, for the same wattage generator, the engine brands chosen for the generators tend to change over time. The diesel engine is in a Yanmar YM2310. The PTO output is rated at 23 HP. The engine HP is about 27 HP. I say about because I have seen the output rated from 23 to 28 HP. If the PTO is rated at 23 HP the engine must be rated higher. So I'll settle on 27 HP.
But the engines will only be under a partial load, say 8 HP. So with a light load will the diesel use less fuel than the gas engine? Anybody have more than a gut feeling? Will the diesel use less fuel?
The tractor in question is the first diesel engined anything I have ever owned and I am learning a lot about them. I already have an appreciation for the fuel usage. For the time run and the work accomplished it is way better on fuel usage than my 80 year old Ford 9N gasoline powered tractor. But that's not really a fair comparison considering the side valve engine in the Ford compared to the overhead valves in the Yanmar. But the John Deere riding mower that my wife loves do much to use has a 23 HP overhead valve engine in it and it uses way more fuel per hour than my Yanmar.
Thanks,
Eric

 

[Roadworthy]

This is kind of an apples and oranges comparison but lacking some important details. The rpm or engine speed will probably come into play here as well. A generator is very picky about the speed it runs to put out a specific voltage and frequency. Do you want to compare consumption at idle, full speed, or somewhere in between? Since the proposed diesel engine is half again as powerful as the gasoline example it's not going to be working nearly as hard but you may have to crank the speed up to get the generator up to speed.

 

[alexpops]

Diesels tend to be more finicky in terms of matching the load than gas since they need heat to achieve a clean (full) burn. Too big a diesel for the load at rpm needed to keep the genny at 60hz & you'll have unburned fuel in the stack and the crankcase. Could lead to bearing and valve problems, fouled injectors which will make it worse, not to mention dpf issues if a newer diesel.

 

[LD1]

Too many variables. Because a generator isn't a constant load. Depends on how much stuff it's running.

Also depends on the gas engines.

I only have experience with Kawasaki and Kohler. And between the two of similar HP (23-28) and similar displacement (720-760cc) the Kawasaki's are much more efficient.

I can mow my 4 acre yard with a 61" ZTR with a Kohler right at 2 gallon per hour. 5gal total. Same yard, same weekly mowing conditions....if I use a similar 61" with a kaw, same time to mow...bout half the fuel.

Kohler's are thirsty. Unless you get the fuel injected ones with an O2 sensor. Then they compare nicely with Kawasaki.

With so many variables....I am gonna offer my gut intuition that the gasser is gonna be more efficient, but not much. I'm thinking ,1/2 gal per HR for gas and 3/4 gal per HR for the yanmar

 

[RalphVa]

The subject is my question. How would a 14 HP air cooled gasoline engine compare to an approx. 27 HP liquid cooled diesel engine. I know that on an equal type basis the gas engine is going to use about 20% more fuel than the diesel when powering the same load. But this is not an equal comparison. The gas engine is an overhead valve air cooled generic engine in a Generac generator. I said generic because I'm thinking that all the engines made for this type of work are pretty much the same. Especially since, for the same wattage generator, the engine brands chosen for the generators tend to change over time. The diesel engine is in a Yanmar YM2310. The PTO output is rated at 23 HP. The engine HP is about 27 HP. I say about because I have seen the output rated from 23 to 28 HP. If the PTO is rated at 23 HP the engine must be rated higher. So I'll settle on 27 HP.
But the engines will only be under a partial load, say 8 HP. So with a light load will the diesel use less fuel than the gas engine? Anybody have more than a gut feeling? Will the diesel use less fuel?
The tractor in question is the first diesel engined anything I have ever owned and I am learning a lot about them. I already have an appreciation for the fuel usage. For the time run and the work accomplished it is way better on fuel usage than my 80 year old Ford 9N gasoline powered tractor. But that's not really a fair comparison considering the side valve engine in the Ford compared to the overhead valves in the Yanmar. But the John Deere riding mower that my wife loves do much to use has a 23 HP overhead valve engine in it and it uses way more fuel per hour than my Yanmar.
Thanks,
Eric

Carbureted gas engines use 50% more fuel than non turbo diesel engines. This is from data among us engineers back in the 80s.

A 14 hp gas engine would use the same amount of fuel as a 21 hp diesel.

 

[LittleBill21]

fuel price needs to be factored in as well

 

[Sawyer Rob]

Diesels tend to be more finicky in terms of matching the load than gas since they need heat to achieve a clean (full) burn. Too big a diesel for the load at rpm needed to keep the genny at 60hz & you'll have unburned fuel in the stack and the crankcase. Could lead to bearing and valve problems, fouled injectors which will make it worse, not to mention dpf issues if a newer diesel.

What modern diesel have you seen do this???

I have a 60hp tractor that has had over a thousand hours of raking hay at low rpm, just chugging along at 1100 rpm, barely loaded hour after hour and it never has wet stacked one bit.

I've seen other tractors, also doing light work for many hours, and none have ever wet stacked.

I would never worry about wet stacking these days....

BTW, I've run my pto genset lightly loaded for hours without any tractor problems at all...

SR

 

[pmsmechanic]

What modern diesel have you seen do this???

I have a 60hp tractor that has had over a thousand hours of raking hay at low rpm, just chugging along at 1100 rpm, barely loaded hour after hour and it never has wet stacked one bit.

I've seen other tractors, also doing light work for many hours, and none have ever wet stacked.

I would never worry about wet stacking these days....

BTW, I've run my pto genset lightly loaded for hours without any tractor problems at all...

SR

Well I have a 2004 4410 that blew some crap out the exhaust after a particularly cold winter of pushing and blowing snow. I didn't think it was light work but there was a wet streak down the exhaust after rototilling the first garden.

 

[etpm]

Thanks everybody for your replies. Even with the relatively poor fuel economy of the 14 HP engine on my generator I had a feeling that it wasn't bad enough to merit pressing my little diesel tractor into service as a generator power source. The responses here confirmed that. But it always helps to get second and third opinions from folks who know.
Thanks Again,
Eric