Is their a noticable difference gas vs diesel

[RobJ]

The thing about gas combustion is when the air/fuel mixture explodes, it "slaps" the piston and the slight pressure of the expanding air forces the piston down. On the other hand, when a diesel compresses all that air and forces fuel into it at very high pressure, the combustion is more of a burn rather than an explosion and this slow burn will constantly push the piston all the way down rather than just hitting it like a gas explosion.

A spark or a high temps due to pressure, both fuels explode when ignighted. The only reason diesel fuel goes in to the chamber at a high pressure is to atomize the fuel for a more complete burn. The pressure is needed to force it through a small orifice, think car wash.

Diesels get their low end torque because the engine itself is under more load to compress the air at a higher compression. So you have bigger/heavier pistons, rods, cranks and flywheels, blocks, etc(anyone remember the Olds gas conversion to diesel engine?). Because of all this mass, it has a tendency to stay in motion, but this also limits the rpm range of the engine.

New designs are allowing for higher revving diesels, I don't know much of anything about those and their hp/torque curves.

 

[Dmace]

A spark or a high temps due to pressure, both fuels explode when ignighted.

It is all subject to the how the term "explode" is used. All explosions are just rapid burning but still Diesel does NOT explode, it burns.

About Cars - all about diesel engines
Direct quote from above article:

Diesel fuel doesn't explode; instead it burns, and the expanding gasses push the cylinder down.

The only reason diesel fuel goes in to the chamber at a high pressure is to atomize the fuel for a more complete burn.

So, you are saying that you could run a diesel engine with the same fuel pressure as a gas engine.
The air in the combustion chamber of a diesel engine is under 1.5-2 times as much compression (18:1-20:1 compared to 8:1-10:1) and that is why you need higher pressure fuel. The atomizing helps but surely is NOT The only reason.

 

[RobJ]

So, you are saying that you could run a diesel engine with the same fuel pressure as a gas engine.
[/I]

Nope

Ok I'll edit, you know what the normal PSI reading is on a diesel engine. I don't know off the top of my head either. the gas engines I worked on were about 150psi I think, so maybe a diesel is 300, 400? Dunno. Snap on makes a guage for Cats and some deeres that's 0-800psi. Fuel pressure at the injector is about 2000psi (generic injector pop off spec). To better burn the fuel it needs to be turned into fog. My guess is Rudy had a problem with this early on because while combustion ignition works, maybe it's not the most effeicient way, thus the fuel needs to be broken down into fine particles so it can ignite easier and burn more completly. It doesn't take 2000psi to overcome the pressure in the cylinder.

Hey remember its the internet...Aaron Gold?

 

[Egon]

Ahh - I dunno -

Gasoline- diesel - LPG - ng-- Chances are they can all be designed to produce torque at certain RPM ranges.

I seem to recall some natural gas engines running at 300 rpm Max 360 days a year For the last 50 years!

Don't know what lasts longer!

 

[RobJ]

I seem to recall some natural gas engines running at 300 rpm Max 360 days a year For the last 50 years!

those are the big 1 cylinder units running oil well pumps, using scrubbed NG from the well. The piston is about 18-24" round. You can hear them for miles at night, but I'd rather not.

 

[Egon]

Nope; they were a two cycle natural gas engine running natural gas compressors. Some were v6 and others were v10. Cooper Bessemer was the make. Engine and compressor were integral. Some had turbos and others did not.

 

[john_bud]

I've seen a lot of stuff posted, some correct some less than correct. IMHO.

Diesel is a slow burning fuel. Gasoline is an explosively fast burning fuel. At low RPM's you can put more diesel fuel into the combustion process and the combustion pressures don't spike so high that the engine fails. Diesel is burning as the the piston goes down, giving consistently higher pressures thru a greater percentage of the combustion stroke. That is why diesels have more low end torque.

Gasoline being a fast burning fuel allows the engine to rev up to higher RPM's. After about 4500 rpms there is not enough time for the diesel fuel to all burn and adding more fuel just results in more unburnt fuel out the exhaust. But on a gasoline engine that shorter time decreases the pressure spike caused by the extra fuel. Gas engines can rev up to what, 12,000-15,000 rpms and still be effective at converting fuel to rotational energy. Not that I like the buzzing sounds of those engines....


Back to the OP's question. A gas 50 hp engine and a diesel 50 hp engine will be very similar in operation in ag equipment. Ag equipment is designed such that the high speed benefits of gasoline are minimized and the low speed benefits of diesel are maximized. That allows for the diesel to be more efficient converting fuel to rotational energy. The end result is that you use less fuel with the diesel engine, usually 30-50% less. Some designs had especially good diesel engines and not so good gas engines and the consumption difference was 100% or more! Not a big deal when gas was 19.9 a gallon.

Some of the inaccuracies I noted are really just old information. Injection of diesel fuel now takes place with 22,000-25,000 psi. That atomizes the fuel much better than the old 2000-2500 psi for a pop-off injector. Result is finer control, better combustion completion and thus higher efficiency. Injectors are now electro-mechanical devices able to give several bursts of fuel at precise times in the combustion process. The quiet in the diesels we have today is due to small correctly timed precise volumes of fuel in the pre-combustion phase.

Of note, lots of work is ongoing to raise gasoline injection pressures into the same region. That will allow for multiple direct injections of fuel, even while the piston is on the way down. That will give the next generation gas engines low end torque superior to any diesel engine and still have the high rpm capability. Oh, they will probably not have any need for spark plugs either (compression fired with 20:1 ratios) and the high volatility of gasoline will mean that they will start much easier in the winter than a diesel. You also won't have to worry about fuel gelling.

Who wants a small block v8 with 750 ft-lb of torque from 1300 rpm all the way up to 7500 rpm? Wait until the camshaft, lifter, pushrod and rocker arms are eliminated in favor of electro-mechanical linear actuators that are able to vary the valve timing, valve open distance and duration with software. Imagine having the perfect cam profile for each and every rpm and load condition. That same theoretical engine would idle smoother than mom's old Buick and rip asphalt better than a 426 hemi on steroids. And with active fuel management turning off cylinders, keeping the exhaust valves open and the intakes closed to minimize pumping loss -- fuel economy will exceed that of diesel too.

Who doesn't like technology? My only fear is that Microsquash will program the controllers! Shudder...

 

[MossRoad]

I was wondering if you had a gas tractor with 50pto hp and a diesel with 50 pto hp is their a difference?

I know a diesel has more torque on a wider band and longevity is much higher motor wise. just wondering?

I just happened to have owned a 50PTO HP 4 cylinder GAS engine tractor for 10 years. It was a late 70's International Harvestor 2500B tractor loader. That is, it had a permanently mounted front end loader and a 3pt hitch. (Also had a nice warm cab).

It was rated at 50 PTO HP and when the engine was at PTO speed of 540 it was turning about 2400 RPM. It was not much different than a diesel powered unit in that respect.

As I was told by many folks here on TBN, 50HP is 50HP. So no difference there, either.

It had many thousands of hours on it and had never been rebuilt, however, I am pretty sure that a diesel would last much longer and use less fuel.

On another note, it was also HST tranny. With the HST tranny, you had to run it at higher RPMs as stated in the manual to keep pressure on the pumps in the tranny. That increased the fuel usage as compared to a gear tranny tractor. I never measured the fuel usage, but do know that I could put a 5 gallon can of gas in it and run it for several hours at high RPMs.

Hope that helps.

 

[flusher]

The gas engine will need to run at much higher rpms to make the same power as a diesel engine, this means more fuel consumption and more wear and tear which leads to shorter engine life. One pro of the gas engine is it's ease of cold weather starting. A simple plug makes my diesels start even easier then the gassers though.

QUOTE]

Hmmm!

Ford 8N, gasoline, 4 cyl, 120 cid, 27.3 hp (pto) @ 1500 rpm
Kubota L3430, diesel, 3 cyl, 100 cid, 28.5 hp (pto) @ 2700 rpm.

Don't know if this is pertinant, but there seem to be plenty of 50+ year old 8N gassers around my neck of the woods doing an honest day's work.

 

[chh]

(quote=flusher) Don't know if this is pertinant, but there seem to be plenty of 50+ year old 8N gassers around my neck of the woods doing an honest day's work.


As the old saying goes, They just don't build them like they used to.

Seems like no one believes an engine can run that slow anymore.