Big, slow, gasoline engines?

[Stelth]

I've wondered why big, slow, diesel engines are common, and gasoline engines tend to run much faster. For instance, a diesel-electric locomotive might have an engine that runs flat-out at 900 rpm. Big diesel trucks commonly shift at 1800 or so rpm.

In comparison, the Ford GAA, which is kind of a big, slow gasoline engine, would rev to 2600-2800 rpm in stock trim, and the International 549, one of the last big gasoline truck engines, would rev to 3400-3600 rpm. And I shouldn't forget the GMC 702 V12 making 250 hp at 2400 rpm.

But then, there are the diesel behemoths like the Wärtsilä-Sulzer RTA96-C, which powers container ships and tops out at 102 rpm, running on heavy fuel oil.

Why are there no modern gasoline giants? Or are there some that I don't know about?

 

[Colt45ws]

They are less efficient. No reason to.

 

[RamFan]

I'm trying to figure out why you'd want a big and slow gas engine, even diesel for that matter.

 

[punisher]

Big and slow was by necessity, not choice.

 

[JTK]

Originally Posted By: Stelth

Why are there no modern gasoline giants? Or are there some that I don't know about?


I believe it's because the thermodynamics are such that they consume more fuel then a comparable diesel would.

 

[A_Harman]

In the case of very large bore engines, gasoline engines have classically had detonation problems when the bore size goes above 6". Flame propagation occurs at the same rate in gasoline combustion, regardless of the cylinder size, so there is more time for end gases to heat up to autoignition temperature in a large bore engine. Automotive engines that we are accustomed to talking about are in the range of 3-4.25" bores.

The diesel combustion process does not have a limit on cylinder bore size because flame initiates in many different locations in the cylinder at the same time.

 

[Errtt]

Engineering, design & materials.
Locomotive diesels, i.e. GE 7FDL16A7 may run @ 900rpm, we've ran em up to 1200rpm.
Large diesels, straignt-8s, 6s, (Coopers, Wakukesha, BLM Baldwin-Lima-Hamilton, Enterprise DSQ-38s & up, etc.), can run at much lower rpm. I don't think I'd want to be around one with the weight of the pistons etc., screaming beyond design over-speed rpm's.
If those injectors were spark plugs, watch out.

 

[Spazdog]

Jay Leno's Blastolene Special has a 29 liter engine that redlines at something like 2800 rpm. ( just a few hundred rpm higher than the turbodiesel variant of the same Continental engine that powered my tank)

The 6 cylinder eta variants of the 3 and 5 series BMWs had low redlines (and they were big compared to the four cylinders that Honda and Toyota were making)

 

[SwampSurvivor]

Originally Posted By: RamFan
I'm trying to figure out why you'd want a big and slow gas engine, even diesel for that matter.


Most 18 wheeler diesels redline at 2100 RPM. They can start out in 1st gear, with a fully loaded trailer without giving it any throttle. Diesel engines, by nature, have high torque at low RPMS and a very narrow power band.

The pistons in the OTR truck diesels are HUGE. I wouldn't want to be spinning them at 6000RPM like a car engine.

Having a slow turning , high torque gas engine is nice when towing as well - way easier to get going than having to wind it up to 6000RPM.

Also nice when on a trail as you're not constantly on the clutch and it can just idle along content.

I do like my high revving aluminum 4 cylinder, but there are days where I wish it had the same torque curve as my AMC I6

 

[Chris142]

A huge hall scott in a semi truck back in the 50's would get 3 mpg but a cummins Diesel would get 6 ,have more torque and less parts to fail plus diesel wass Practically free back then.

 

[RamFan]

Originally Posted By: Miller88
Originally Posted By: RamFan
I'm trying to figure out why you'd want a big and slow gas engine, even diesel for that matter.


Most 18 wheeler diesels redline at 2100 RPM. They can start out in 1st gear, with a fully loaded trailer without giving it any throttle. Diesel engines, by nature, have high torque at low RPMS and a very narrow power band.

The pistons in the OTR truck diesels are HUGE. I wouldn't want to be spinning them at 6000RPM like a car engine.

Having a slow turning , high torque gas engine is nice when towing as well - way easier to get going than having to wind it up to 6000RPM.

Also nice when on a trail as you're not constantly on the clutch and it can just idle along content.

I do like my high revving aluminum 4 cylinder, but there are days where I wish it had the same torque curve as my AMC I6


Thanks for the response. I guess the 250hp rating op mentioned threw me for a loop. Reminded me of the 7.5l V8 F250 I had. Big engine, big appetite, low rpm range; wouldn't want an engine like that again. Just no need for a 10mpg when today's can perform better while drinking less.

 

[Rick in PA]

If you ever want to see some really big, really slow running engines, go to Rough and Tumble Historical Association in Lancaster, PA. I highly recommend the Thresherman's Reunion, in mid-August, that's when they have everything running.

I've pondered the evolution of power plants, from slow running steam engines to high RPM gas turbines. Higher RPM power plants always pack more "punch", that roots back to the equation E=MV^2. My take is that it took time to develop the technology to increase the RPMs. There also had to be a need, as the cost is generally greater. A helicopter wouldn't fly well on a diesel engine, but put a turbine in it, and off it goes. I seem to remember the turbine driven turbopumps in the space shuttle had some very impressive numbers, for both power and RPMs.

I know there are exceptions, but I'm just looking in general.

 

[SwampSurvivor]

Originally Posted By: RamFan
Originally Posted By: Miller88
Originally Posted By: RamFan
I'm trying to figure out why you'd want a big and slow gas engine, even diesel for that matter.


Most 18 wheeler diesels redline at 2100 RPM. They can start out in 1st gear, with a fully loaded trailer without giving it any throttle. Diesel engines, by nature, have high torque at low RPMS and a very narrow power band.

The pistons in the OTR truck diesels are HUGE. I wouldn't want to be spinning them at 6000RPM like a car engine.

Having a slow turning , high torque gas engine is nice when towing as well - way easier to get going than having to wind it up to 6000RPM.

Also nice when on a trail as you're not constantly on the clutch and it can just idle along content.

I do like my high revving aluminum 4 cylinder, but there are days where I wish it had the same torque curve as my AMC I6


Thanks for the response. I guess the 250hp rating op mentioned threw me for a loop. Reminded me of the 7.5l V8 F250 I had. Big engine, big appetite, low rpm range; wouldn't want an engine like that again. Just no need for a 10mpg when today's can perform better while drinking less.


Yup! They all have nothing crazy for Horsepower but well over 1000 ft/lb of torque. The big difference is because of the super narrow power band.

 

[Stelth]

Originally Posted By: A_Harman
In the case of very large bore engines, gasoline engines have classically had detonation problems when the bore size goes above 6". Flame propagation occurs at the same rate in gasoline combustion, regardless of the cylinder size, so there is more time for end gases to heat up to autoignition temperature in a large bore engine. Automotive engines that we are accustomed to talking about are in the range of 3-4.25" bores.

The diesel combustion process does not have a limit on cylinder bore size because flame initiates in many different locations in the cylinder at the same time.


I thought it was probably something like that. I know some of the really big gasoline engines have two or more spark plugs. Here's one with 4 spark plugs per cylinder, and 3619 cubic inches (59.3 l) displacement:



Video is a stationary engine that was used for water pumping, but I think it's basically the same engine that was used in the Coast Guard 83 footer. The Coast Guard boat used two, and they were straight 8's making 600 hp each at 1200 rpm.

I just find big, slow, hi-torque engines interesting and wondered if gasoline was at all competitive in that arena. I guess not, but I think natural gas is making headway.

 

[zloveraz]

If you want 425 HP, at least 630 lb-ft of torque on 87 pump gas you can get one today...

http://www.thunderv12.com/power

 

[Cujet]

Don't forget modern, air cooled, aircraft engines. They are generally limited to 2700 RPM, and some have redlines considerably lower. Certain Mooney aircraft redline at 2400 or 2500RPM. Some Cessna aircraft are now as low as 2200RPM. (mostly for noise reasons, but also efficiency)

Aircraft engines, with modern injection systems and electronic ignition are regularly capable of 0.36Lb fuel/HP/HR. A BSFC number that is on par with modern diesel engines.

The impressive efficiency is due, in part to operating temperatures, piston ring swept area (a key factor) (with lower PRSA being better, lower friction) and the geometry of a large cylinder's heat transfer characteristics (by displacement, one large cylinder has less surface area to transfer heat, and therefore work energy, than multiple small cylinders.

EDIT: Remember, Avgas is 6LB/gal and Jet-A is 6.5. Aircraft fly by weight, not by gallon. So, a gasoline burning aircraft engine with excellent BSFC numbers will still consume more than a diesel, in gallons. Makes little difference in ground transport, but in the air, weight is the only thing that matters.

 

[DrDusty86]

Ford had a 471 CI gas truck engine that was low HP, low RPM and HIGH torque for its day.

 

[IndyIan]

Gas tractors used to be common in the 40's and 50's. I don't know how big they got, 80hp?
My buddy has a 1951 gas TEA-20 with 28hp @ 2000rpm, from a 2.1L 4cyl. He goes through some gas while brush hogging but I think its comparable to my 2011 41hp diesel which actually runs a bit faster, 2400rpm.

 

[Stelth]

Originally Posted By: zloveraz

If you want 425 HP, at least 630 lb-ft of torque on 87 pump gas you can get one today...

http://www.thunderv12.com/power


That would be a blast in a T-bucket.

 

[TiredTrucker]

Originally Posted By: Stelth
I've wondered why big, slow, diesel engines are common, and gasoline engines tend to run much faster. For instance, a diesel-electric locomotive might have an engine that runs flat-out at 900 rpm. Big diesel trucks commonly shift at 1800 or so rpm.

In comparison, the Ford GAA, which is kind of a big, slow gasoline engine, would rev to 2600-2800 rpm in stock trim, and the International 549, one of the last big gasoline truck engines, would rev to 3400-3600 rpm. And I shouldn't forget the GMC 702 V12 making 250 hp at 2400 rpm.

But then, there are the diesel behemoths like the Wärtsilä-Sulzer RTA96-C, which powers container ships and tops out at 102 rpm, running on heavy fuel oil.

Why are there no modern gasoline giants? Or are there some that I don't know about?


I would contend that you are even high on the semi diesels. Many of the latest ones now find their sweet spot between 1100 and 1300 instead of the 1800. The only time I have hit 1800 with my semi is on a down hill side running the engine brake. Typically, I shift up at around 1600 and operate at cruise at around 1425. that is a Series 60 12.7L Detroit. With the new DD15 and ISX, they typically cruise at around 1300-1350 and to take them above 1500 instead of shifting up is not the wisest thing to do for both power and economy.

Let's get at this a little. Torque on a commercial heavy truck diesel peaks at a lot lower RPM, typically 1100 rpm. It starts dropping off above 1500. With the lower compression ratios, smaller displacement of the auto gas engine, and the lower BTU content of gasoline / ethanol fuels compared to diesel, you will not hit max torque until above 4000 rpm.