Why Luftwaffe and Kreigsmarine diesels but petrol Wehrmacht?

Shortround6 said:

A problem for the Germans is when do you convert your gasoline based motor transport system to diesel? Granted rail was still well over 90% coal and river traffic was also mostly coal. But light/medium trucks? And you need to start converting in the mid 1930s (if not earlier) without disrupting production too much.

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The German synthetic fuel plants were mostly using the Bergius process. Which is good for producing decently high octane gasoline; the B4 avgas was AFAIU more or less straight Bergius process output + a smattering of TEL (and lead scavenger, ethylene bromide maybe?). However, if you want diesel-type fuels the Fischer-Tropsch process AFAIU can produce fuel with considerable less capital outlay than the Bergius process can produce either gasoline or diesel. So if Germany wanted to pivot to diesel, it's not only about developing the engines but probably they would need to build more Fischer-Tropsch plants instead of Bergius plants. They would still need some Bergius plants for AVGAS production, and for whatever land-based gasoline demand was remaining (cars & motorcycles etc. even if trucks and tanks were running on diesel?). But they could probably save quite a lot of capital cost with this change. In any case, if it's going to have any impact on WWII yes they would need to start many years previously. At the very latest the moment the nazis take power they would have needed to start the diesel transition.

As for railways and river barges, by all means continue with coal. Works well enough, and is not dependent on capital intensive synthetic fuel facilities.

WARSPITER said:

View attachment 778923
The Kreigsmarine could have done with one of these then ? 25,480 litre diesel. Get yours today.

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Would that baby even fit under the citadel roof?

Jokes aside, for warships you'd be looking at medium speed diesels for improved power/weight, and much smaller size. A large slow revving two-stroke uniflow diesel as in this picture, impressive as it is, is not what you want for pushing towards 30 knots top speed or beyond.

Admiral Beez said:

Wasn't the USMC diesel-powered in the PTO? Why?

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AFAIU the motivation was logistics. The USMC already had a lot of other diesel powered equipment (landing craft etc.) so they already had the logistics chain for diesel fuel setup. Similarly the US Army in Europe didn't want diesel tanks, as they felt the advantage of standardizing fuel supply outweighed the advantages of a diesel.

z42 said:

AFAIU the motivation was logistics. The USMC already had a lot of other diesel powered equipment (landing craft etc.) so they already had the logistics chain for diesel fuel setup. Similarly the US Army in Europe didn't want diesel tanks, as they felt the advantage of standardizing fuel supply outweighed the advantages of a diesel.

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I suppose a wider use of diesel engines led Canada's Valentine tanks to go to the USSR.

z42 said:

Would that baby even fit under the citadel roof?

Jokes aside, for warships you'd be looking at medium speed diesels for improved power/weight, and much smaller size. A large slow revving two-stroke uniflow diesel as in this picture, impressive as it is, is not what you want for pushing towards 30 knots top speed or beyond.

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The pictured diesel, in it's larger (longer) 14 cylinder form, is actually heavier per horse power than the British steam plant the British dropped into the modernized Queen Elizabeth battleships. Not by much but still? In fact it is around 18-19% heavier per HP than the machinery used in the KGVs.
Now use 1940-41 Diesel engines, use smaller/shorter cylinders do you can shorten the engine to something a lot closer to 10 meters height (or lower) , which means more cylinders and longer engine (actually multiple engines) and then..........................
Yes you get fantastic fuel economy, but you need something like the H class battleships to fit the engines in.
Germans were a little too willing to push the envelope of ship engine design to get the paper specs they wanted. They paid for in it unreliability.

It is one thing for an S-boat to loose an engine 20km off the Dutch coast. It is another for a long range cruiser to have trouble thousands of km from home. Germans tried for a bit too much speed in their destroyers. Trying to fit 70,000hp in a destroyer hull, even with light weight machinery forced a bunch of design compromises.

Getting back to the tank engines. the German HL230 seems to have weighed around 2000lbs or close to it. The Ford V-8 was just under 1500lbs and was aluminum. It was longer than the German V-12? (measured how?) Not sure if the Germans included the clutch.
German engine used SOHC and two valves per cylinder, Ford V-8 used DOHC and 4 valves per cylinder. Ford was 18 liters driving a low/mid 30 ton tank.
M-26 tanks had a less successful relationship with the engine. Maybe because they were trying to drive a 45 ton tank with it?

Shortround6 said:

The pictured diesel, in it's larger (longer) 14 cylinder form, is actually heavier per horse power than the British steam plant the British dropped into the modernized Queen Elizabeth battleships. Not by much but still? In fact it is around 18-19% heavier per HP than the machinery used in the KGVs.
Now use 1940-41 Diesel engines, use smaller/shorter cylinders do you can shorten the engine to something a lot closer to 10 meters height (or lower) , which means more cylinders and longer engine (actually multiple engines) and then..........................
Yes you get fantastic fuel economy, but you need something like the H class battleships to fit the engines in.

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Yes, as mentioned for warships slow speed diesels is not what you want. They are amazing for fuel efficiency and reliability, which is why they're the standard in big ocean-going cargo ships these days, but power/weight is not their forte. For faster ships, you should be looking at medium speed diesels (max rpm in the 300-1000 range), widely used in things like passenger ships, other smaller ships, railway engines etc. A few medium speed diesels (& KGV steam plant) examples for comparison:


Going by this, by the late 1930'ies the Germans had marine diesels that far surpassed capital ship steam plants in terms of power/weight. One wonders if they had been better off staying the course with diesels instead of pivoting to high pressure steam..

For more info on the MAN marine diesels see MAN Double-Acting Diesel Marine Engines .

Germans were a little too willing to push the envelope of ship engine design to get the paper specs they wanted. They paid for in it unreliability.

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Arguably the German penchant for fancy engineering caused problems. There are reasons why double-acting cylinders, as used in those MAN pre-war/WWII marine diesels, weren't successful in internal combustion engines, despite being widely used in steam engines. For comparison all the contemporary medium speed diesels in the table above are plain "boring" single-acting four-stroke diesels (including the MAN 9L used in the QE2 refit).

Another issue was that these MAN engines AFAIU ran on diesel, not bunker fuel. There were marine diesels running on bunker fuel already in the interwar years, but AFAIU for medium speed engines that took off only after WWII.

Germans tried for a bit too much speed in their destroyers. Trying to fit 70,000hp in a destroyer hull, even with light weight machinery forced a bunch of design compromises.

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They tried too much in general with their destroyers. Like putting 6" guns and other equipment on them making them very top heavy and atrocious sea boats. Luckily the world got rid of a lot of them in Narvik.

Getting back to the tank engines.

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Wrt German diesel engines for tanks, this again seems to be a case of German overly fancy engineering. Porsche designed their dream tank engine, a X-16 air cooled affair, but it never got anywhere before the war ended. Just do a frickin' boring water cooled four-stroke V-12, a well known and mature concept, and go with that!

z42 said:

Yes, as mentioned for warships slow speed diesels is not what you want. They are amazing for fuel efficiency and reliability, which is why they're the standard in big ocean-going cargo ships these days, but power/weight is not their forte. For faster ships, you should be looking at medium speed diesels (max rpm in the 300-1000 range), widely used in things like passenger ships, other smaller ships, railway engines etc. A few medium speed diesels (& KGV steam plant) examples for comparison:

Engine	When	Power	Weight	RPM	Used where	Power/weight
UK BB steam plant	~1936	82 MW	2700 tons	-	KGV class	30 kW/ton
MAN M9Z 42/58	~1928	2.5 MW	110 tons	450	Deuschland class	23 kW/ton
MAN V12Z 32/44	~1940	11.9 MW (turbocharged)	66 tons	600	Destroyer (never built)	180 kW/ton

Going by this, by the late 1930'ies the Germans had marine diesels that far surpassed capital ship steam plants in terms of power/weight. One wonders if they had been better off staying the course with diesels instead of pivoting to high pressure steam..

They tried too much in general with their destroyers. Like putting 6" guns and other equipment on them making them very top heavy and atrocious sea boats. Luckily the world got rid of a lot of them in Narvik.

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A couple minor corrections:

Unfortunately, 2 cycle diesels need a blower (supercharger) to ensure air flows the correct direction. To make the required 54,000hp for the Deutschland class ships, that would have required 11 cylinder engines + blower (M11Z 42/58). Which was longer than the available space in the hull, but the diesels were narrow. So MAN had a plan: If they split off the blowers and 2 cylinder from each pair of diesels, the engines were only 9 cylinders long, which fit in the hull - M9Z 42/58. As there beam available, they built a 5 cylinder engine (2 cylinder for each main engine + 1 to power the engine itself) and attached the blower for all 3 engines to this. So, you really need to take the weight of the main engine + 1/2 of the auxiliary engine + supercharger when calculating power.

Also, the 110 ton diesels in Deutschland were too light and had to be reinforced. By time of Admiral Graf Spee, the engines had gained 15 tons (and were still cracking mounts).

Deutschland class diesels each make 7,100 hp = 5.25 MW before the gear boxes.

I haven't figured out how to merge cells

What the numbers don't show is the space/manpower requirements. While 21st century diesel need very few men to operate, the MAN diesels need more men than a steam plant.
As for space - The Panzerschiffe D class could fit 100k hp of HP steam in the same space as 80k hp of diesel. So, while the diesels themselves might be making better power to weight, after you add in the extra hull length and required armour, the numbers get much closer. And when "Standard" displacement doesn't care about fuel fraction, HP steam looks good.

While I don't disagree than the KM tried to do too much with their destroyer, they are no more top heavy than Fletcher class DDs. What made them atrocious sea boats was an attempt to make them faster.

If you watch Fletcher class DD at top speed, you will note the stern is "digging a hole" in the water, there is a "rooster tail" and the bow is attempting to plane. All very inefficient for a displacement hull. So, the KM designers tried to be cute: They designed the stern to lift and set the propellers up so they wouldn't create the rooster tail. The result is the bow stays down and they got an extra knot or 2.

The problem is the set up works all the time. So, in a seaway at cruise speed, the stern is still trying to lift/force the bow down. But in a seaway, they last thing you want is the bow down...

Back to tank engines - the problem isn't making the power - its making the power in the available space. Needing another couple bogies and armour to allow the fitting of a larger (longer) diesel defeats the purpose.

z42 said:

Going by this, by the late 1930'ies the Germans had marine diesels that far surpassed capital ship steam plants in terms of power/weight. One wonders if they had been better off staying the course with diesels instead of pivoting to high pressure steam..

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We have two areas of confusion here. Not including time.
Steam powerplants were usually divided by class of ship. Cruisers used lighter powerplants per hp that capitol ships and Destroyers used even lighter machinery.
For instance the HMS Belfast got 80,000hp from about 1500 tons. Almost 40kw/ton? British H Class destroyers were 34,000hp for 490 tons. H class destroyers were NOT particularly sophisticated/advanced.
The Admiral Hipper would have needed 18 engines from the Deutschland class, 6 engines on each of 3 shafts?
BTW I think somebody made a typo on power output of M9Z 42/58, 7100hp should be 5,294kw not 2,494kw?

Also note that powerplant weight is not engine weight. Powerplant weight includes reduction gears, pumps and "stuff" that is needed to make the power.
Aux generators are not counted (usually) and ventilation, etc may not be.
Individual engine weight gives a wrong impression.

The other source of confusion is planned/proposed vs actual. The tonnage may have been close, the actual reliability is suspect.
A lot of steam plants had trouble when they pushed things too far. Not just the Germans. and what was do-able varied almost by the year. What you could do with steam changed several times between 1920 and 1942. British were getting 50,000hp out of two boilers in a Battle class Destroyer.
The other thing for warships was the square footage of the machinery spaces. Which affects hull size and compartmentation. Some countries squeezed things a little too tight making maintenance difficult and emergency repairs very difficult.

don4331 said:

Unfortunately, 2 cycle diesels need a blower (supercharger) to ensure air flows the correct direction. To make the required 54,000hp for the Deutschland class ships, that would have required 11 cylinder engines + blower (M11Z 42/58). Which was longer than the available space in the hull, but the diesels were narrow. So MAN had a plan: If they split off the blowers and 2 cylinder from each pair of diesels, the engines were only 9 cylinders long, which fit in the hull - M9Z 42/58. As there beam available, they built a 5 cylinder engine (2 cylinder for each main engine + 1 to power the engine itself) and attached the blower for all 3 engines to this. So, you really need to take the weight of the main engine + 1/2 of the auxiliary engine + supercharger when calculating power.

Also, the 110 ton diesels in Deutschland were too light and had to be reinforced. By time of Admiral Graf Spee, the engines had gained 15 tons (and were still cracking mounts).

Deutschland class diesels each make 7,100 hp = 5.25 MW before the gear boxes.

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True, I hadn't included the compressor engines, but in fairness they can't be left out either. I added them to my table in the above post.

Back to tank engines - the problem isn't making the power - its making the power in the available space. Needing another couple bogies and armour to allow the fitting of a larger (longer) diesel defeats the purpose.

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Depends on how much longer it is. But yes, it's probably going to be slightly longer than the equivalent petrol engine. Shorter length is an advantage of a water cooled engine, but they wanted air cooled, which might have been a factor in the decision to go for the X-16 layout in the Porsche diesel tank engine instead of a V-12.

Shortround6 said:

The Admiral Hipper would have needed 18 engines from the Deutschland class, 6 engines on each of 3 shafts?

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Hippers were later, so they could have used more advanced diesel engines, had they decided to continue pursuing diesel?

BTW I think somebody made a typo on power output of M9Z 42/58, 7100hp should be 5,294kw not 2,494kw?

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Oh, you're right! I had just copy-pasted that number from the oldmachinepress page without checking whether it made sense. I'll fire off an email to the admin.

(and if you want to nitpick, it's probably 7100 metric horsepower, thus 5222 kW.)

Also note that powerplant weight is not engine weight. Powerplant weight includes reduction gears, pumps and "stuff" that is needed to make the power.
Aux generators are not counted (usually) and ventilation, etc may not be.
Individual engine weight gives a wrong impression.

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Good point. I added the figures for just the core engine components (boilers, turbines, presumably condensers too) to the KGV row. If you use that for calculating the KGV results do get a bit better, and probably closer to an apples-to-apples comparison.

don4331 said:

Back to tank engines - the problem isn't making the power - its making the power in the available space. Needing another couple bogies and armour to allow the fitting of a larger (longer) diesel defeats the purpose.

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It can be a bit of both, it also shows the problem of comparing "modern" engines (of any sort) with pre-WW II or WW II engines.

A GMC 6-71 diesel made about 175hp in the WW II era, it weighed about 2200lbs depending on exact model and accessories. Or more than the German HL230 610-639hp engine.
It was also longer by around 25cm? The Diesel Sherman used two of them. Wonder how a Panther would have performed with two engines
In 1958? they were not only making the -71s in 3, 4, and 6 cylinder models, they were making V-6s, V-8s and V-12s. Some of the fire trucks I drove (late 70s) had V-6s and V-8s. The V-6 had about 250hp and the V-8 had 325hp, Power could be changed by changing the injectors. By the time production was stopped in 1990s due to pollution controls, the later 0-92 series
V-6 was rated at 552hp using twin turbos. Lots of luck getting 400hp out of WW II 6-71.

Shortround6 said:

It can be a bit of both, it also shows the problem of comparing "modern" engines (of any sort) with pre-WW II or WW II engines.

A GMC 6-71 diesel made about 175hp in the WW II era, it weighed about 2200lbs depending on exact model and accessories. Or more than the German HL230 610-639hp engine.
It was also longer by around 25cm? The Diesel Sherman used two of them. Wonder how a Panther would have performed with two engines
In 1958? they were not only making the -71s in 3, 4, and 6 cylinder models, they were making V-6s, V-8s and V-12s. Some of the fire trucks I drove (late 70s) had V-6s and V-8s. The V-6 had about 250hp and the V-8 had 325hp, Power could be changed by changing the injectors. By the time production was stopped in 1990s due to pollution controls, the later 0-92 series
V-6 was rated at 552hp using twin turbos. Lots of luck getting 400hp out of WW II 6-71.

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Getting better power/weight from a WWII era diesel engine wasn't impossible, good as the American 71 series was. The Russian V-2 used in almost all their tanks, weighted around 750 kg, and depending on version produced somewhere between 450 and 600 hp during WWII. The most common version used in the T-34 produced 500 hp.

WARSPITER said:

View attachment 778923
The Kreigsmarine could have done with one of these then ? 25,480 litre diesel. Get yours today.

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Turn it sideways and it might work in a further-upsized Landkreuzer P. 1000 Ratte.

z42 said:

Getting better power/weight from a WWII era diesel engine wasn't impossible, good as the American 71 series was. The Russian V-2 used in almost all their tanks, weighted around 750 kg, and depending on version produced somewhere between 450 and 600 hp during WWII. The most common version used in the T-34 produced 500 hp.

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A lot depends on the expected engine life that the customers want. Also depends on the availability of raw materials.
The 71 series was cast iron, it was used in over the road trucks and in small locomotives and for a bunch of industrial applications. It was expected to last for thousands of hours.
1970-90 military versions were pushed and were set up for fast engine changes.

You can sometimes find power ratings for some diesel engines based on intended use. Like stationary power plant, Work boat, road use, emergency vehicle, military, Sport boat.
Military is usually the most powerful. Modern military has mobile cranes to help with engine swaps in the field.

The Soviets had converted an Aluminum aircraft engine. It was light, cost is unknown. It was about 50% longer than the German gas engine (which was freakishly short). Soviets also didn't have as much choice. They couldn't always make new stuff. They had to adapt old stuff most of the time because they didn't have the tooling to make the new tooling for new stuff. They could adapt but starting from square one was very hard for them. They did some amazing things, but a lot of the time it might not have been their first choice if they had had a clean sheet of paper.

GM cracked a lot of blocks with their 1970s diesel conversion, but can it be done well?

The V-12 Rolls-Royce Meteor tank engine was re-designed into the V-8 Meteorite with a diesel variant.

Though 240 hp isn't much use.




View: https://www.youtube.com/watch?v=9VQe9Ahk9d8

Shortround6 said:

A lot depends on the expected engine life that the customers want.

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That's true. But maybe the V-2 was good enough, considering the expected lifetime of a tank on the Eastern front? Decades of trouble-free operation in civilian use is perhaps not a particularly relevant design criterion for a WWII tank engine?

But it seems the soviets never changed that design philosophy after WWII when they were no longer standing with their backs against the wall. During the cold war, Soviet equipment definitely had a reputation for ruggedness in the sense they could often easily be fixed by rather basic means. But they were also often maintenance hogs and with little thought spent on crew ergonomics.

The Soviets had converted an Aluminum aircraft engine.

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In the tank engine thread Best tank engines of WWII it was claimed that the V-2 was not based on the H-S aero engine, except perhaps very remotely in the sense of the persons involved having connections with people knowledgeable about the H-S or the BMW VI aero engines that were the basis of the Soviet inline aero engines.

Shortround6 said:

Getting back to the tank engines. the German HL230 seems to have weighed around 2000lbs or close to it. The Ford V-8 was just under 1500lbs and was aluminum. It was longer than the German V-12? (measured how?) Not sure if the Germans included the clutch.
German engine used SOHC and two valves per cylinder, Ford V-8 used DOHC and 4 valves per cylinder. Ford was 18 liters driving a low/mid 30 ton tank.
M-26 tanks had a less successful relationship with the engine. Maybe because they were trying to drive a 45 ton tank with it?

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For the HL230 I have
Weight 3080 lbs Width: 100cm Height: 119cm Length: 131cm

Wiki had the GAA as a 60 degree V8, since it was based off the Ford V12

Weight 1470 lbs Width: 84cm Height: 121cm Length: 150cm Difference seems to be the clutch

Thank you, I found about 2080lbs weight for the HL230 on net, typo or?

Shortround6 said:

Thank you, I found about 2080lbs weight for the HL230 on net, typo or?

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Panther & Its Variants by Walter Spielgerberger, p.232 lists weight of HL230 as 1,200 kg (dry); 3,080lbs would match HL230 and cooling unit weight

don4331 said:

Panther & Its Variants by Walter Spielgerberger, p.232 lists weight of HL230 as 1,200 kg (dry); 3,080lbs would match HL230 and cooling unit weight

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Haven't been able to find the wet weight of the GAA, and US practice didn't typically include radiator weight.

So is hard to get an exact apple to apple comparison.

Upthread, I had the M6 powerplant, the Wright G200 of 1820 cubic inches, a 9 cylinder radial, roughly twice the displacement of the R-975 Continental used in the M4 series at first.

It was both 55" wide as was tall, since it was a radial, after all. That's about 140cm vs the Maybachs 100cm and 119cm tall.
It was only 52" long, that 132cm, not so far off from the length of the Maybach.

The big saving was on weight, 1350 pounds dry, and 1771 pounds wet, that's the oil, being aircooled.

It did have a far better output. 800rpm@2300rpm and 1850 ft-lbs torque at the same speed. That was with the governor set, running free, it was 960hp.

Don't need eight gears for that kind of torque, but transmission strength was an issue: the US didn't have a dry plate clutch to handle that kind of power in 1941
This led to the electric drive and hydramatic and torque converter transmissions, as was thought to be faster to get into service than to develop a conventional geared transmission and clutch.

Another plan for the unbuilt T1E3, to have four 6-71 diesels, with a pair driving its own hydramatic transmission.

Now the electric drive did add over three tons to the weight.
While Aberdeen did complain about the brakes during testing, seems to have been far more reliable than the Henschel or Porsche Tiger Prototypes the Nazis would be testing months later.

Shortround6 said:

A GMC 6-71 diesel made about 175hp in the WW II era, it weighed about 2200lbs depending on exact model and accessories. Or more than the German HL230 610-639hp engine.
It was also longer by around 25cm? The Diesel Sherman used two of them. Wonder how a Panther would have performed with two engines
In 1958? they were not only making the -71s in 3, 4, and 6 cylinder models, they were making V-6s, V-8s and V-12s. Some of the fire trucks I drove (late 70s) had V-6s and V-8s. The V-6 had about 250hp and the V-8 had 325hp, Power could be changed by changing the injectors. By the time production was stopped in 1990s due to pollution controls, the later 0-92 series
V-6 was rated at 552hp using twin turbos. Lots of luck getting 400hp out of WW II 6-71.

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GM's EMD did offer a big V8 diesel from the Naval subchasers, the 8V-184, with as with the -71 or -96, the displacement of each cylinder
so that was 1471 cubic inches. It was half of the X block

600HP@1800rpm 1910 ft.lbs torque at 1000rpm 3750 pounds dry
in Tank ready form, used in the M4A2E1, a stretched hull even longer than the M4A6
By this time, The US had strong enough clutch and gearbox that electric drive wasn't needed.

In addition to dieselization, an interesting naval propulsion what-if is drastically more powerful boilers. In particular, in 1933 the RN tried a Velox boiler from the Swiss BBC for a destroyer, promising an order of magnitude improvement in steam generation per floor area. Despite this test, at around the same time the RN decided to standardize on the Admiralty pattern boiler, so nothing came of it. But what if they had gone down that path?

And how did the Velox boiler achieve such power density? Well, BBC had the idea to compress the incoming air (=more heat generation per volume), and increase the velocity of the flue gasses. Ok, so add a compressor to compress the incoming air. And how to drive the compressor? Well, there's quite a lot of energy in those flue gasses, so what about a (drumroll..) turbine wheel? I guess you can see where this is going. Now with the technology of the day there wasn't much excess power available after running the compressor (presumably required a lot of extra air to avoid melting the turbine blades with the available alloys, inefficient blade design etc.), so it was clearly a boiler and not a gas turbine engine.

But if one of the big navies had gone for this system in the early thirties and shoveled R&D money into it, we could have had gas turbines a few years sooner, with interesting ramifications both for WWII naval ships as well as aircraft.