Modern Gas Tractor? What's the Chance?

[Ricn]

One of my Dad's 3 tractors was a JD 1020 gasser he bought new. I still have it today and she purrs along like new. I run it often during the summer and never leave gas in it for very long, a pain sometimes but it keeps things cleaner and is much easier to start. Tune ups are easy as well. Small tractors running on gas would be good I think but in todays world it looks like battery units is all we will have and sooner than later.

 

[mo1]

I wouldn't give up the reliability of a mechanical diesel for a gas engine

Even if you go mechanical injection, you still have spark equipment to worry about

Then fuel burn. My 22hp lawnmower burns gas at the same rate my 50hp diesel tractor burns fuel. And the tractor covers a lot more acerage per hour, 46in deck vs 84

I would never consider it.

A gasoline engine is usually a lot simpler than a diesel engine.

That lawnmower probably has a simple air-cooled carbureted engine with a magneto firing the spark plugs. Even if it's an EFI lawn mower engine (which should burn noticeably less fuel than a 50 HP diesel tractor if the tractor is doing more than just driving around), it would have simple port fuel injection at about 30-60 PSI driven by a simple fuel pump, and a mass-air or speed-density EFI that's been used for several decades on road vehicles with very few issues beyond the very first generation of units. A mechanical diesel is going to be water-cooled and have an expensive, finely-machined injection pump to inject the fuel at a couple thousand PSI, and depending on the engine, it may or may not have a turbocharger and aftercooler.

New mechanical diesel engines are basically limited to 25 HP and under. Essentially all new diesel engines >25 HP are high-pressure common-rail computer-controlled engines injecting fuel at 20,000+ PSI. At a minimum (>25 to <76 HP) they have either EGR and a catalyst or no EGR and a combination soot trap/catalyst. Ones >75 HP are all of that and have a urea catalyst (DEF and SCR) as well. A modern road gasoline engine at worst has the same turbocharger and aftercooler setup a diesel would, but the direct injection on the gasser runs at mechanical diesel injection pressures rather than the far higher Tier 4 common-rail pressures. Gassers usually don't have EGR any more, and their catalysts are a ton simpler than any >25 HP diesel's setup. There are also a lot of naturally-aspirated port-injected road gas engines that are not much more complicated than an EFI lawnmower engine.

 

[milkman636]

Yes, I’d like a naturally aspirated, port injected gasoline powered tractor. That would be a simple, clean burning, low fuel pressure, long life, type of machine.

It should last like my current gasoline powered vehicles that are between 11 and 19 years old that use the same technology. They get driven every day and have thousands of hours on them. 200,000 miles on my truck is roughly equivalent to 7000 hours. What’s there to be afraid of?

 

[mo1]

Yes, I’d like a naturally aspirated, port injected gasoline powered tractor. That would be a simple, clean burning, low fuel pressure, long life, type of machine.

It should last like my current gasoline powered vehicles that are between 11 and 19 years old that use the same technology. They get driven every day and have thousands of hours on them. 200,000 miles on my truck is roughly equivalent to 7000 hours. What’s there to be afraid of?

The thing they are afraid of is that it will take some significant engineering costs to make the design modifications to convert an existing diesel engine design on gasoline, and more costs yet to come up with a new gasoline engine design. They worry that the governments will carry through on their promises to force everything to be battery-powered and be stuck with having sunk money into developing a gasoline engine that is now unsalable.

In general if you have a modern compression ratio in the nines on a port fuel injected gasoline industrial engine you will get a continuous power rating of about 21-22 HP/L at a rated speed of 2500 RPM with two-valve heads and 25-26 HP/L at 2500 RPM if you have four-valve heads. A naturally-aspirated two-valve diesel running at those same speeds is usually about 19 HP/L. I picked that speed as that's similar to what diesels run at and thus would lead to just as long of a lifespan. Now, tractor diesels can have a continuous rating of 40 HP/L or so with multiple turbos and four-valve heads, so you would need to use a much larger displacement engine to make the same power with a NA gasser as a higher-powered turbodiesel. It would be doable but may need an increase in chassis size to accommodate the engine, or moving to a different engine design such as a V-6 gasser to fit where a four-cylinder diesel was. That and you may have a shorter-stroke design to let the gasser rev higher (usually 3600 RPM is the redline on a continuous-rated industrial gasser) to make low to mid 30s HP/L depending on heads.

Turbocharging a gas engine in an industrial situation would require a very high octane fuel with port injection, which is why the current spark-ignition tractor designs with turbochargers run on ~120 octane natural gas. You could run less octane with a turbocharged DI gasser, but I have yet to see one of those being used industrially.