Diesel vs gas

[buickanddeere]

Back in the 70's I was working as an engineer for Cleaner Combines. We used the same basic engine gas or diesel but the gas wouldn't handle slugs fed into the combine like a diesel. Slug -- poor -- dead -- dig the slug out. So we changed to GM gas engines to get more gas engine power. Combine 155 HP from a Chef 350 gas or 130 from a turbo 301 Allis-Chalmers. Same result except sucking a tremendous amount extra fuel when fuel prices were skyrocketing with $1 per gallon in site. Bit the bullet and dropped the gas, or rather the customers did it for us.

I have a Kubota M7-171 rated by Kubota at 140 PTO up. The Nebraska test shows it put out slightly more HP at the E PTO 1600 rpm than it did at the rated PTO 2000 rpm. Since HP=2 × pi x T/33,000 the torque has to really climb to get more HP at 1600 than at 2000. Our JD 7720 is even better rated at 130 PTO but by the Nebraska test peaking at 170 HP as it pulls down.

I grew up with Far all H's and M's but what a difference when we got our first diesel - except for starting at 40 below. It didn't, but the Farmalls were still around.

Check you formula and math . The HP does not increase as the engine luggs down to the torque peak.

 

[ovrszd]

Have a look at the tachometer on a 4020 gas and a 4020 diesel. The gasser makes more HP per cubic inch at the same 1900 rpm for PTO. The 4020 gasser is not turning 3500-4500rpm.

I was referring to his trucks.

 

[ovrszd]

Nah. My late 70's IH2500b had a gas engine and PTO speed was about 2400rpm, as I recall. I'll have to pull the manual and check it.

Jeez, another one. I was referring to his trucks.

 

[ovrszd]

I remember hearing about a well drilling rig around here. The got it with a Dodge V10, and it got like 3mpg for them. Needless to say; they got a Cummins when the V10 mysteriously burned up. I think the B5.9t got like 12mpg or so. Not too surprising. Those 8.0ls were always thirsty.

And turned twice the rpms.

 

[MossRoad]

I was referring to his trucks.

Jeez, another one. I was referring to his trucks.

This is a tractor forum! :laughing:

 

[ovrszd]

This is a tractor forum! :laughing:

I didn't mention trucks, he did.

 

[MHarryE]

Please do a little research on modern mid and large ag tractor engines. Its been a long time since torque backup has been so large on diesels that there is a horsepower increase. I was in error citing the numbers on our 7720. The real numbers are 141.89 horsepower at 2100 rated engine speed and maximum horsepower is 159.69 at 1650 rpm. That is 355 lb-ft @ 2100 and 511 lb-ft @ 1650 or an excellent 44% torque backup. You don't see that kind of torque backup in SCUTs or CUTs but its expected in mid and large ag although I don't recall seeing any tractor bettering our 7720s 43%. Having 30% backup is considered a minimum.

At Gleaner we established a constant horsepower from rated engine speed to peak torque. This insured we had adequate torque backup for tough spots. Then we were purchased by Deutz who dictated, "We do not care about your requirements, this is the engine you will use". Things went downhill from there.

By the way my avatar is a diesel cycle explaining why a diesel has more pulling power than a gas engine although with proper equipment a gas engine can be built to nearly match a diesel.


Here is a simplified explanation from GrainNews:


Torque Rise Explained - Grainews

 

[Texasmark]

Biggest difference is torque: lots more with diesel, probably a result of the higher compression ratio.

I don't know where compression plays into it other than to get x number of hp out of a given space. The compression on a diesel generates heat as the air is compressed (compression ignition). The heat is what explodes the fuel vapor since there is no spark plug like in a (spark ignition system). That's why low compression engines, needing overhaul are "addicted" to ether. The older they get the worse the compression the harder to start.....the addiction thing has nothing to do with ether, it's all about compression. Diesels usually are under square with a long stroke and the purpose it to have a long burn period of the fuel to keep the foot-lbs flowing and to help in developing the compression ratio.....that's why 2 strokers are low on torque for the engine size and have to run high rpms.....Old OMC outboards at 25 hp were 30 cu in and ran 4500 rpm. Mercs ran 1 cu in/hp and up and ran at 5500-6000. Half way down the power stroke (every rev on them) the exhaust ports open and out goes the charge. If you didn't get the bang out of your fuel by then you just lost it.

Remembering hot rods of the 60's where they ran 10:1 compression and had to run high test, premium fuel to prevent self detonation, pre-igniton, pinging, or what ever you want to call it. High compression "Edelbrock" for a name got more bang out of a given block due to more compression.

 

[MossRoad]

I didn't mention trucks, he did.

DOH! :laughing:

 

[MossRoad]

Please do a little research on modern mid and large ag tractor engines. Its been a long time since torque backup has been so large on diesels that there is a horsepower increase. I was in error citing the numbers on our 7720. The real numbers are 141.89 horsepower at 2100 rated engine speed and maximum horsepower is 159.69 at 1650 rpm. That is 355 lb-ft @ 2100 and 511 lb-ft @ 1650 or an excellent 44% torque backup. You don't see that kind of torque backup in SCUTs or CUTs but its expected in mid and large ag although I don't recall seeing any tractor bettering our 7720s 43%. Having 30% backup is considered a minimum.

At Gleaner we established a constant horsepower from rated engine speed to peak torque. This insured we had adequate torque backup for tough spots. Then we were purchased by Deutz who dictated, "We do not care about your requirements, this is the engine you will use". Things went downhill from there.

By the way my avatar is a diesel cycle explaining why a diesel has more pulling power than a gas engine although with proper equipment a gas engine can be built to nearly match a diesel.


Here is a simplified explanation from GrainNews:


Torque Rise Explained - Grainews

I think I get it, but what's the difference between torque rise and just fudging the numbers to under-rate an engine's specs so it seems like you're getting some magical power out of it more than it's rated for?

 

[VroomVroom]

I know you can't compare with different transmissions, different size tires, engines......just curious of the comparison between my fathers farmall M, 43 hp , 1953 I believe and the little 2816hst I bought for my mother. As a kid, I was always amazed at what that old farmall would pull. And then discovering it only had 40 hp or there about. Now I see this little engine about 14 or 16 inches long in that Mahindra, diesel powered with 28 hp and wondered how far in pulling power it would have compared to the farmall. Since my father passed away I haven't had the chance to get the farmall out of storage to compare. Or haul any big wagons with the little compact tractor. The shear weight of the farmall, its just a bigger tractor and that's that. The big wheels and probably not far off of over 1.8 times the weight of the little compact. When my father said they got that after using horses it was thought of as a massive powerful tractor. Its a 40 hp gas and the compact is a 28 hp diesel.

Also, the J5 we use sometimes. they have a 115 hp gas engine, flathead 6. Years later they made some of them with a 4 cylinder diesel perkins with 90 or 100 hp. I wondered what the comparison would have been.

 

[buickanddeere]

And turned twice the rpms.

The V10 was not a direct injection gasser and the Cummins was not a tier IV diesel .

 

[buickanddeere]

I don't know where compression plays into it other than to get x number of hp out of a given space. The compression on a diesel generates heat as the air is compressed (compression ignition). The heat is what explodes the fuel vapor since there is no spark plug like in a (spark ignition system). That's why low compression engines, needing overhaul are "addicted" to ether. The older they get the worse the compression the harder to start.....the addiction thing has nothing to do with ether, it's all about compression. Diesels usually are under square with a long stroke and the purpose it to have a long burn period of the fuel to keep the foot-lbs flowing and to help in developing the compression ratio.....that's why 2 strokers are low on torque for the engine size and have to run high rpms.....Old OMC outboards at 25 hp were 30 cu in and ran 4500 rpm. Mercs ran 1 cu in/hp and up and ran at 5500-6000. Half way down the power stroke (every rev on them) the exhaust ports open and out goes the charge. If you didn't get the bang out of your fuel by then you just lost it.

Remembering hot rods of the 60's where they ran 10:1 compression and had to run high test, premium fuel to prevent self detonation, pre-igniton, pinging, or what ever you want to call it. High compression "Edelbrock" for a name got more bang out of a given block due to more compression.

Diesels tends to be under square are the long stoke is required to obtain enough compression ratio. It is much more difficult to obtain 18 to 1 with an undersquare vs and over square engine .

 

[buickanddeere]

87 - octane gas is about $3.50/gal now in CA; diesel is over $4. You prob have to go to Hawaii
to find prices that high in the US.

I notice that the smallest diesel engine sold now in CA (in new excavators) seems to be 3-cyl, Yanmar, Kubota, or
similar, and only about 10 hp and a bit over 700cc. A 420cc gas engine (CARB/EPA-compliant) puts out 15-16hp.

If the tier IV emissions regulations had not been relaxed for diesels under 25 HP . Diesels under 25HP would be very expensive and rarely used .

 

[buickanddeere]

Check you formula and math . The HP does not increase as the engine luggs down to the torque peak.

Well I should have said with natural aspirated diesels and turbo diesels without electronic control . Yes it is possible to tweak turbo boost , cam timing and injection timing to make a diesel 田onstant HP from it痴 菟eak torque rpm to it 菟eak HP rpm.

 

[buickanddeere]

Somewhere the question was raised about a 2018 direst injection gasser vs a 2018 tire IV diesel in medium to HD applications .
The efficient per BTU of fuel would be about a wash with the gasser haviing the advantage at less than 100% load and the diesel with a slight advantage at continuous 100% power .
Diesel Fuel due to being “heavier” contains more carbon per gallon and contains approx 111% of the energy a gallon of gasoline does .
Diesel however does not burn as clean as gasoline . Something similar to propane burning cleaner than gasoline as it’s a “lighter” fuel than gasoline . Something to consider with the cost of particulate filters, urea injection, EGR cooler etc . Plus the fuel filters, glow plugs, , extra batteries etc .

 

[ovrszd]

The V10 was not a direct injection gasser and the Cummins was not a tier IV diesel .

Please explain how that makes a difference?

 

[dfkrug]

If the tier IV emissions regulations had not been relaxed for diesels under 25 HP . Diesels under 25HP would be very expensive and rarely used .

And indeed that is what has happened. A quick search for small single cylinder Tier IV EPA-compliant engines yields 2 makes sold in the US: Hatz and Kohler. Neither seem to be CARB-compliant, so not available in CA. Also, the former, in electric-start, is over $3K + tax and shipping. Very expensive and rarely used! A CARB/EPA compliant gas engine is under 1/10 the cost.

I just went thru trying to import a non-compliant 11hp ChangChai diesel engine in a mini-X. Many folks have gotten around the EPA inspection, but I could not. Attached is the EPA Form 3520.

 

[Snobdds]

Duty cycle on Diesels are much lower than on gas motors.

The diesel can work half as hard to produce the same power, which is reflected in RPM's.

Diesels always win in this debate...

 

[MossRoad]

Duty cycle on Diesels are much lower than on gas motors.

The diesel can work half as hard to produce the same power, which is reflected in RPM's.

Diesels always win in this debate...

That's a blanket statement that is proven incorrect a couple times. See the engine specs on my IH2500b with both gas and diesel engines that I posted earlier. The gas engine is smaller, produces the same power, at a tad lower RPMs.