16 replies to this topic

[mariner]

Again from my favourite enginelabs site a new opposed piston engine but from the Giant Cummins operation.

 

The concept is of course far from new buI don't think it hast been used for new engine for many years 

 

https://www.enginela...stons-per-hole/

 

To be used in US military vehicles so one would assume it has been properly tested etc.

[desmo]

Should work fine, I don't see any likely real world advantages vs. a conventional 2-stroke CI.

[Greg Locock]

Heat loss through the cylinder head is a big deal in diesels. I was involved with various ill fated attempts to turn SI engines into CI, and even when the bottom end was strong enough, they always overheated.

[blueprint2002]

The only similar engine that I recall, in the automotive world, was the Commer TS3 of 1954 onwards. It was built that way so that it could be fitted under the floor of a coach; see “The Commercial Motor” of 7 May that year. It had only one crankshaft, operated by six conrods whose small ends were on rocking levers, whose opposite ends were in turn connected to the pistons. Sorry I am unable to post an attachment.

One advantage of the opposed-piston layout was that perfect balance of the reciprocating parts was possible, regardless of the cylinder numbers. And it was suited to the two-stroke because inlet and exhaust port timing, being controlled by separate pistons, could be adjusted to give somewhat better performance.

Junkers Jumo and Napier Deltic were two earlier diesels using the same principle, the former for aircraft and the latter for rail traction and marine propulsion.

Fairbanks-Morse and Doxford built much bigger, slower-running marine diesels of similar concept, for a number of years.

This new engine should be just as good, if not better.

[manolis]

Hello all.

 

 

Question:

Is there a real innovation / advantage of the Cummins / Achates Power opposed-piston engine design (1,000HP, 14.3L, combat):

 

 

 

as compared to the old Junkers Jumo opposed-piston engines of 1930’s ?

 

 

Spot on their capacities and their power outputs.

 

 

 

Hello Mariner.

 

You write:

“To be used in US military vehicles so one would assume it has been properly tested etc.”

 

After spending several millions of US dollars, Achates Power ended up with this prototype for drive tests (the video is of Nov 2018):

 

 

Now Achates Power comes back (with Cummins) with a military engine i.e. an engine that needs not to comply with emission etc regulations.

 

This reminds the “story” of the EcoMotors / OPOC (funded, among others, by Bill Gates) that after spending some 100million US dollars (several of them from the US Army), they changed their goal from making “the most eco friendly engine ever” to just making a working / reliable engine for gen-sets, before completely disappearing.   

 

 

 

In comparison, the “pulling rod architecture” of the pattakon opposed-piston engines brings real differences.

 

The pulling rod architecture:

extends substantially the dwell of the piston at its combustion dead center,

provides more time to the combustion to complete at higher expansion ratios,

transfers the thrust loads to the cool / ports-free side of the cylinder liner,

reduces  the specific lube consumption,

prevents the scuffing etc, etc.

 

 

Here is the opposed-piston OPRE Diesel engine (more at https://www.pattakon...attakonOPRE.htm ) :

 

 

 

Here is the single crankshaft PatOP opposed-piston Diesel engine (more at https://www.pattakon...ttakonPatOP.htm ) :

 

 

 

Here is the spark ignition OPRE Tilting engine ( more at https://www.pattakon...akonTilting.htm ) :

 

 

 

 

 

Hello Blueprint2002.

 

You write:

"The only similar engine that I recall, in the automotive world, was the Commer TS3 of 1954 onwards. . . . Sorry I am unable to post an attachment."

 

 

Here is an animation of the Commer TS3:

 

 

The (blue) rocker arms are extra-over-loaded, their central pivots suffer, etc, etc. Despite its problems, it was a successful design.

 

Compare the Commer TS3 design with the single-crankshaft PatOP Diesel engine:

 

 

(the big diameter piston, at right, is the “built-in” “direct-drive” scavenge pump).

 

Thanks

Manolis Pattakos

 

[Charlieman]

To be used in US military vehicles so one would assume it has been properly tested etc.

My recollection is that military vehicle engines built during the cold war were specified for 100 hours of flat out running before a major service. The logic of the day was that conventional warfare would be conducted for three days...

[blueprint2002]

Should work fine, I don't see any likely real world advantages vs. a conventional 2-stroke CI.

 

Without any valve gear, such an engine is a lot quieter than is usual. I have some experience of a 16 cylinder marine diesel of USSR origin, and can confirm that this is actually the case. 

[blueprint2002]

Hello all.

 

 

Here is an animation of the Commer TS3:

 

Thanks Manolis. A picture is worth a thousand words, they say. An animation must be worth a million words.

[gruntguru]

Without any valve gear, such an engine is a lot quieter than is usual. I have some experience of a 16 cylinder marine diesel of USSR origin, and can confirm that this is actually the case. 

I wonder if the OP design also reduces noise? Diesel "knock" will radiate mostly through piston crowns then crankcase since there is no cylinder head.

[manolis]

Hello Gruntguru.

 

You write:

“I wonder if the OP design also reduces noise? Diesel "knock" will radiate mostly through piston crowns then crankcase since there is no cylinder head.”

 

 

With same pistons, same piston stroke and same number of pistons,

a non-opposed-piston 2-stroke emits from its crankcase about the same (with the equivalent opposed-piston) Diesel “knock”.

But the non-opposed-piston engine emits a lot of additional Diesel “knock” directly from its cylinder head(s), making it substantially noisier (high frequency noise).

 

A 4-stroke compression ignition needs more (or bigger) pistons to make the same power with the 2-stroke, and therefore it emits more Diesel “knock” from its crankcase and more Diesel “knock” from its cylinder head(s).

 

 

The transmission between the crankshafts of a typical opposed-piston engine creates another kind of noise that increases the total noise emitted by the engine:

 

 

Junkers Jumo:

 

 

 

An opposed-piston having a unique crankshaft,

 

say, like the PatOP:

 

 

or like the EcoMotors OPOC:

 

 

or like the PatPOC (more at https://www.pattakon...takonPatPOC.htm) :

 

 

seems the best solution as regards the Diesel “knock” and the rest noise from the engine.

 

Thanks

Manolis Pattakos

[gruntguru]

Hi Manolis. Is there any difference in length of the engine measured along the cylinder axis - comparing a twin crank solution to the Pat OP or POC?

 

Otherwise the biggest difference seems to be a large rotating mass (Jumo, Achates) versus a large reciprocating mass (single crank solutions).

[manolis]

Hello Gruntguru.

 

You write:

“Is there any difference in length of the engine measured along the cylinder axis - comparing a twin crank solution to the Pat OP or POC?

Otherwise the biggest difference seems to be a large rotating mass (Jumo, Achates) versus a large reciprocating mass (single crank solutions).”

 

 

 

With 64+64=128mm combined stroke, the single crankshaft PatOP prototype (635cc cylinder capacity, 850cc scavenge pump capacity):

 

 

has a total height of 500mm, including the built-in direct-drive scavenge pump.

 

With 50+50=100mm combined stroke, the two-crankshaft OPRE prototype:

 

 

has the same total “height” (500mm), including its two built-in direct-drive scavenge pumps.

 

I.e. the single crankshaft “pulling rod” opposed-piston architecture enables some 20% reduction of the maximum dimension.

 

 

Worth to mention here:

 

The built-in direct-drive scavenge pump of the PatOP, OPRE and OPRE_Tilting opposed-piston engines reduces not only the weight, the external dimensions and (substantially) the overall cost, but it also saves energy (consumed as friction in the gearing from the crankshaft to the scavenge pump of the typical opposed piston).

Think how simply and efficiently the piston-type scavenge pump of the pattakon opposed piston engines is driven: a part of the energy on the combustion-side of the piston passes directly to the scavenge-side of the same piston.

 

For comparison see the external scavenge pump of the Commer TS3 at right, and compare its size (and cost?) to the rest engine (its bore is shown at left) :

 

 

See also the external scavenge pump of the Achates Power 2.7lt (SAE announcement of 2017, for the production of the OP engine developed by Achates Power) :

 

 

 

 

The following quote was posted to another forum (March 2014) :

 

“A couple of years ago I wrote in “TheKneeSlider” where they were re-re-re-presenting the “promising” OPOC engine:

“In EcoMotors they have the funds, they have the publicity (every time a guy in EcoMotors “coughs”, every magazine in the world publishes -or reproduces- an article for OPOC), they have the support (only the name of Bill Gates “opens” every door). What they don’t have is a good engine design.

Unless I am wrong, after several years there is not yet an OPOC in a car or truck for tests by an independent third party.
 

Get in the place of the independent inventors / researchers / makers and think how they feel seeing in the press, again and again and again, about the OPOC of EcoMotors, about how many parts less than the other engines it comprises (which is a false claim), about how many less fuel it will consume (which is also a false claim), about how “green” it will be (which is also a false claim), and so on.””

 

 

Does the above remind something?

 

Differently: make a search on how many magazines and forums published articles about the Cumming / Achates Power combat engine (or about the rest Achates Power opposed piston engines), and reading the articles try to figure out what is the real advantage of these engines as compared to contemporary and older (Junkers Jumo) designs.

 

Thanks

Manolis Pattakos

[blueprint2002]

1. The charging piston, or scavenging piston if you prefer, has been used successfully in the past. DKW’s very fast 250 2-stroke racing motorcycles of the late thirties, were among the best examples. Some had the charging cylinder at right angles to the power cylinder, some had it parallel. This was probably in order to fit into the very confined space on a motorcycle.

A few low-speed marine two-stroke diesels also used this system, often with the scavenge pump driven by an additional crank. This was not uncommon during the 1920s and 30s. The Werkspoor-Lugt engine of the early 50s is a more recent example, in this case with the scavenge piston (one to each power cylinder) driven by a linkage from the crosshead.

But the majority of marine two-strokes have used Rootes blowers or centrifugal blowers for scavenging. In recent years, say since 1980, the centrifugal blower is almost exclusively used (Detroit Diesel being a notable exception, with Rootes blowers for much longer).

 

2. A few marine OP engines have used side connecting rods to couple the upper piston with the crankshaft. Doxford was probably the main exponent of this system, for 50 or more years. But they are not noted for reliable, trouble-free running, or for ease of access for servicing. Most marine OP engines have connected the two crankshafts with a train of gears, and with considerable success, as attested by the results obtained by Fairbanks-Morse, among others.

 

All that is in the past, of course. The future might be different.

Edited by blueprint2002, 25 August 2020 - 06:32.

[manolis]

Hello Blueprint2002

 

The piston type scavenge pumps were known more than a century ago.

I.e. the innovation of the OPRE and PatOP engines is not on using piston type scavenge pumps.

 

 

Here are some DKW piston-type scavenge pumps (superchargers):

 

 

 

The following is quote from the PatPOC web page at https://www.pattakon.com/pattakonPatPOC.htm :

 

Starting with the Junkers-Doxford engine: (**** Fig. 4 shows the big diameter scavenge piston which is integral with the small diameter upper piston 51 in FIg. 5) 

 

 

(heavy unbalanced 2nd order inertia force, long crankshaft especially for multicylinders inline, long connecting rods) and replacing:

- the upper piston and piston pin by a shorter-lighter piston (the piston skirt is only to cover and uncover the ports and not to transfer thrust loads to the cylinder liner) and a reciprocating frame (green),
- the long side-connecting-rods by normal-size connecting-rods at the bottom (not at the sides) of the cylinder,
- the long/heavy wrist pin of the upper piston by a conventional pin that bridges the two lower connecting rods,

the PatPOC engine results.

 

 

In case of symmetrical timing of the ports (crankpins at 0 and 180 degrees), the connecting rods remain constantly parallel to each other, resulting in:

-full balance of the inertia forces and moments of the single-cylinder opposed-piston PatPOC basic module (the reciprocating assemblies are of equal mass).
-zero total force on the crankshaft main journals from both: the combustion loads and the inertia loads .
-compact and lighter design: the short crankshaft (the side connecting rods and crankpins can be arranged inside the cylinder footprint because the "green" frame is arranged normally to the crankshaft axis) enables more compact multicylinder arrangements, like the in-line-three, the in-line four etc. For instance, the PatPOC three in-line arrangment allows significant space and weight saving as compared to the old three in-line Junkers-Doxford marine engines.
To further reduce the width of the PatPOC twin (animation at the top of the page) the central main crankshaft journal (which is rid of inertia and combustion loads) can be eliminated, enabling as small as desirable cylinder to cylinder pitch.

In case of asymmetrical timing of the ports (crankpins at 5 and 175 degrees, for instance, for a 10 degrees advance of the exhaust piston), the resulting unbalanced inertia force of the PatPOC is several times smaller than the unbalanced inertia force of the conventional Junkers-Doxford of same stroke and of same reciprocating mass.
The OPOC (Opposed Cylinder Opposed Piston) engine of EcoMotors cannot help causing an unbalanced 2nd order inertia moment created by the offset between the two opposed cylinders; thereby, the vibration-free quality of the PatPOC single-cylinder basic-module is comparable to that of the OPOC two-cylinder basic-module: the PatPOC is slightly better for small asymmetry of the port-timing, the OPOC is slightly better for bigger asymmetry of the port-timing.”

 

End of quote

 

 

Several excellent photos from the Doxford shipyard, like:

 

 

are available at 

https://www.shipsnos...302549&slide=10

 

Do take a look.

 

 

The piston type scavenge pumps, known long ago, perfectly fit with the “pulling rod” / “crosshead” design of the OPRE, OPRE_Tilting and PatOP engines.

 

Thanks

Manoilis Pattakos

[malbear]

Heat loss through the cylinder head is a big deal in diesels. I was involved with various ill fated attempts to turn SI engines into CI, and even when the bottom end was strong enough, they always overheated.

was the camshaft altered? presumably a bit less overlap due to higher compression bringing the piston crown closer to the valves. . was the exhaust opening made a little bit more conservative say exhaust open a bit later  50 BBDC  instead of 70BBDC on petrol.

[Greg Locock]

I think the only thing they left untouched was the block. They (BL) did eventually produce a reasonable CI conversion of an SI engine, by getting Perkins to do the whole job. 

[Kelpiecross]

was the camshaft altered? presumably a bit less overlap due to higher compression bringing the piston crown closer to the valves. . was the exhaust opening made a little bit more conservative say exhaust open a bit later  50 BBDC  instead of 70BBDC on petrol.

 

 Diesels have shorter duration than SI - one of the main reasons is than a diesel with SI  valve timing would not develop enough cylinder pressure  at starter cranking speeds to actually start.    You would think that a diesel would be a prime candidate for variable duration etc. valve timing.