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Diesel vs gasoline
Posted: Tue Mar 07, 2023 10:14 am
by Eugen
Moved this discussion here from Pictures...
Consider this guys, so everybody and their brother want a diesel engine. Let's take this little G5200 as an example. We can expect a little more torque from the diesel engine, as compared to the Kohler K321, but how much? And you have a three cylinder engine, which at some point you will have to rebuild. Somehow I think the one cylinder Kohler is easier to rebuild and cheaper, please correct me if I'm wrong. On the other hand, maybe you save money on fuel with this diesel engine? I have doubts about that too. The other thing is, the availability and price of attachments for the Case is much better around here. For me Case wins big time.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 11:17 am
by Gordy
Eugen wrote: ↑Tue Mar 07, 2023 10:14 am
@FUTZ I am drooling looking at that bbq! That Kubota G5200 has the 14hp 3cyl diesel engine. In all honesty though, I would not trade my 444 for it, even not knowing what @Spike188 just said, but more so now.
Consider this guys, so everybody and their brother want a diesel engine. Let's take this little G5200 as an example. We can expect a little more torque from the diesel engine, as compared to the Kohler K321, but how much? And you have a three cylinder engine, which at some point you will have to rebuild. Somehow I think the one cylinder Kohler is easier to rebuild and cheaper, please correct me if I'm wrong. On the other hand, maybe you save money on fuel with this diesel engine? I have doubts about that too. The other thing is, the availability and price of attachments for the Case is much better around here. For me Case wins big time.
On the other site someone did a diesel swap. I recall him saying what would have taken a full tank of fuel with the Onan, took 1/3 of a tank with the diesel.
Gordy
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 11:43 am
by Eugen
Gordy wrote: ↑Tue Mar 07, 2023 11:17 am
On the other site someone did a diesel swap. I recall him saying what would have taken a full tank of fuel with the Onan, took 1/3 of a tank with the diesel.
Gordy
Same HP and similar torque? Come on, free energy?
I can believe some difference, but it's hard to believe the Onan is three times as bad in efficiency, producing the same amount of power.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 11:57 am
by Toolslinger
Well, the diesel has 15% more energy per gallon to start with. After that, the diesel engine is likely more thermally effecient... I'm not sure you're going to cut fuel use in a third, but you could for sure do better than the gas engine.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 12:04 pm
by propane1
Kohler K341 16 hp at 3600 rpm, 28.25 ftlb of torque at 2600 rpm.
Shibarua engine, 16 hp at 2700 rpm, 36 ftlb of torque at 1800 rpm
Noel.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 12:11 pm
by Toolslinger
Putting a different pump in to take advantage of the extra torque would help too. Possibly a lot if the machine wasn't really working out at the ragged edge of performance to start with.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 12:13 pm
by propane1
So on PEI. Diesel is at the moment 39 cents more pre litre than gasoline. I’m guessing in some situations it would cost more to run diesel. Maybe.
Quite a difference in compression ratios in a diesel compared to a gasoline engine. Maybe that’s where the diesel gets it’s power in torque.
Noel
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 1:00 pm
by Eugen
It seemed incredible to me, but it's very close to what the theory says. On average a gasoline engine is apparently 20% efficient. That means that with 10 gallons of gasoline you can mow an area of let's say 5 acres. Diesel apparently figures at 40% efficiency, which means that 10 gallons are used to mow twice that area, 10 acres. In other words, if you use one tank of gas with an Onan engine to mow an area, you can expect to use 1/2 the tank with a diesel engine. 1/2 is not one third, but well, we can brush that 16.6% under mathematical error.
OK, fine! I have a Z400 diesel engine (10HP) that I'm thinking of deploying for mower duty.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 1:11 pm
by Toolslinger
Actually that 16% lines up nicely with the additional power density of the diesel fuel.
Re: Pictures: this moment
Posted: Tue Mar 07, 2023 1:20 pm
by Eugen
Toolslinger wrote: ↑Tue Mar 07, 2023 1:11 pm
Actually that 16% lines up nicely with the additional power density of the diesel fuel.
I believe that is taken into account, as 40% is total efficiency (fuel and combustion). I made the numbers look actually better for diesel. The wikipedia article on this says
Diesel engines generally achieve greater fuel efficiency than petrol (gasoline) engines. Passenger car diesel engines have energy efficiency of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. A common margin is 25% more miles per gallon for an efficient turbodiesel.
So, typical would be 30% for diesel and 20% for gasoline.