Vid #93. Diesel vs. Spark Ignition Aero Engines

[@delschmucker794]

I enjoy your through look at the facts around these engine types.

[@Hajduk12]

Excellent video. Thanks for your time and effort.

[@PistonAvatarGuy]

The 320T can be run on mogas and would be absolutely unbeatable if mogas were used in the final comparison. - The 320T data is really surprising to me, all around, and it's great that you were able to get it from Adept. I never would have expected the compression ratio to be so low, I wouldn't have expected the cruise fuel consumption to be so low, and I wouldn't have expected the full power fuel consumption to be so high. I suppose that one can get spoiled after looking at the data from racing engines for many years, as racing engines can manage to have very high compression ratios (even when running on ~90 octane fuel), and very low fuel consumption, all while managing to have high specific power output.

[@arturoeugster2377]

Thanks for sending me the information, appreciate it. Adept is incredible, but gear reduction makes sense. I do have a prototype for a very efficient reduction system . No rubbing teeth, still a positive engaging system, all ball bearings but limited to 1:2, 1:4, 1:8 ratios etc Including load sharing contra rotating applications.

[@PistonAvatarGuy]

@@arturoeugster2377 Positive engagement with no gears? Interesting.

[@arturoeugster2377]

@@PistonAvatarGuy Is is obvious that I cant disclose this over the internet. But there is a rough analogy: and this deals with 2 types of electric motors: 1) the common inductance motor as used on Tesla cars, and the new variable reluctance motor just introduced. 2) Resistance to a current produces power losses I²×R, unavoidable unless it is so cold that super conductivity is there. Reluctance is 'resistance' to a magnetic flux but produces no losses, controlling this allows to properly phase the torque pulses in a motor without losses.The efficiency jumps to ~93%. The key here is to 'think laterally' ,, de emphasize what is known and never questioned, and find Alternate ways to achieve similar but constrained results. In my case only few ratios are possible but the losses are incredibly low. But only a prototype can prove this. The unit can produce coaxial, contra rotating output of high reduction ratios (integers only) Why is that important? Remember Howard Hughes crashed in super efficient twin piston engine A/C with contra rotating props. The rule is: the first prop acts like a normal prop with a peak efficiency ~ 85% (Hamilton Standard, where I used to work), The second prop recovers a part of the losses, the rotation energy, and the rule is this contra rotating one operates at ~100% . In other words, the recovery covers the blade friction losses + -. Both together operate at 92-93%, significant enough to give the Rusky BEAR bomber significantly more range. This old noisy thing is still in use. Applied as single unit to a P&W PT-6 (normally geared down ~ 16:1) would give CR 15:1 exactly. Connected directly to the power turbine. Just saying, no actual plan. BTW 15 = 2 × (8) - 1 CR SR

[@arturoeugster2377]

Reading your remarks a year ago, I am also skeptical that a sfc of 0.33 can be achieved. My speculation is that in cruise they overlean and have a protection for the oversized exhaust valve, combined with extended expansion, by variable timing of this valve(s). That reduces pressure available to the exhaust turbine, but just enough to drive the optimized compressor, and minimizing the waist gate flow, if any. Tremendous progress has been made with CFD on single stage centrifugal compressors (Example the french Microturbo, now part of SAFRAN, has a turbine engine with a single stage pressure ratio of 8, earlier 4 was the 'limit') What that means is, that high total pressure ratios ( compr + piston) are possible, requiring high power operation with much excessive fuel for cooling , like on a TIO-541 Lycoming at TO and climb power. And an optimized piston lubrication system. Maybe asymmetric location of the connection rod bearing on the piston, to reduce side loads. As you know, diesel engines produce soot, which produces graphite coating on the cylinder walls, reducing friction and greatly reducing wear. This has to do with the very high combustion temperatures in diesel engines due to the high compression ratio. The combustion occuring at temperatures much higher than 1000°C produces first carbon monoxide, not co2, only after cooling due to expansion does the temperature drop below 1000°C, then the Boudouard process begins where 2 CO molecules produce 1 molecule of CO2 and free carbon - soot. this process is complete at temperatures of 400°C. Because on a diesel engine there is always excess oxygen available, some of the soot is burned, on the downstroke, explaining the higher thermodynamic efficiency of the diesel engine. Now with over leaning on the Adept engine, together with high turbocharger pressure resulting in higher combustion temperatures an analog process can be visualized, improving the efficiency, diesel like. All this is speculation, a teststand operation of this engine with proper instrumentation, can shed light of what is happening on this remarkable 'clean sheet designed' engine.

[@PistonAvatarGuy]

@@arturoeugster2377 I wouldn't say that I'm skeptical about their SFC number at cruise, I think that it's entirely possible, I'm just surprised that they were able to achieve that number with such a low compression ratio. I've been seeing gasoline engines around 0.36 for years, but they're all running near stoichiometric and have 10:1+ compression ratios, so leaning should provide some additional efficiency. With liquid cooling, the cooling of the exhaust valves wouldn't be a significant concern, your concern no doubt comes from your experience with air-cooled engines. No VVT is used on the Adept Airmotive engine. Your reduction system is very interesting. As a teen (~20 years ago), I often wondered why no one had come up with some sort of electric torque converter (for lack of a better way to describe it), and I'm sure that there are some very real difficulties which have prevented something like that from becoming commonplace. It rarely pays to think 'outside-of-the-box' these days when it comes to well understood technologies, but I wish you luck. I hope that you're not crediting Howard Hughes with the invention of contra-rotating propellers, as they were around long before he ever made use of them. Those engines weren't even developed by any of his companies/employees. I'm not sure which aircraft first used contra-props, but I know that they were very successfully used on the Schneider Trophy aircraft built by Macchi in the early '30s. The XF-11 was very, VERY old news by the time it actually flew, Hughes was trailing very far behind the curve at that time. And while contra-props are efficient, their additional weight, cost and complexity can only rarely be justified, which is why they're almost never used. Even the final version of the XF-11 was built without the problematic contra-props that were used on the first example.

[@zmanmd1641]

Thanks again for an excellent presentation. I assume the Adept 320T is port injected with DOHC and coil on spark ignition, as are most cars were when it was first designed. Using an 120 degrees bank angle should eliminate the need for a power robbing balance shaft. Did the engine use any variable cam timing or were the cams optimized for cruise power (~240 hp)? Finally, the gearing would have to be at least 2.0/1 to use the full 320 HP with most standard propellers. Since whole number reduction ratios risk resonance between the engine and prop, did they go with a still higher ratio so the max power occurs well below 2700 RPM on the propeller? Thanks in advance.

[@rv6ejguy]

Yes, port injected, DOHC, 4 valve, COP as far as I know. I may be doing a more in depth video on these engines again in the future as the company has been in touch again recently. Most V6 engines don't use balance shafts. No VVT on this engine as that doesn't make much difference on an aircraft engine operating at high load and a relatively narrow rpm range. Not sure what the redrive ratio is but probably not 2 to 1 exactly.

[@tuckernielson1]

This is fantastic information. Thank you very much for your time and effort. Do you think you could do an analysis of the Aeromomentum engine offerings?

[@rv6ejguy]

Thank you. Glad you found the video useful. It took a while to research. If Mark at Aeromomentum would share the latest info on his offerings, I'd give it a shot.

[@tuckernielson1]

@@rv6ejguy I'll reach out to Mark.

[@MikeMike-er7kn]

We could throw the various Rotax's (and sds injected version), Viking, Jabiru, ulpower with the Aeromomentum into a similar video to this one!

[@Hellcleaner13]

What's your opinion on Deltahawk's jetA engine?

[@rv6ejguy]

Always just a year away going back 15 years now. So expensive now that's it's not viable for GA. You still can't buy one. Not proven, no dealer network. Doesn't look good to me.

[@gsxr1kmatt]

My RV-10 partner and I were engine shopping at OSH18.. Adept said "production was right around the corner" then too.. Kinda disappointing, I think that engine has a TON of potential.

[@rv6ejguy]

I saw them posting on VAF tonight, looking for an RV-10 to develop a kit on. Post was removed by a mod. I sent a PM telling the Adept guy that they'd have to buy an ad to post. They were delayed a year with the Covid crap in SA.

[@JTGmartin]

Fantastic info, could you add the Higgs diesel and the Delta hawk? I think Higgs also modifies air cooled engines to be water cooled .

[@rv6ejguy]

I could maybe do another segment on these 2 engines in future if the manufacturers were willing to share technical info and photos. Glad you liked this video.

[@SuperYellowsubmarin]

@@rv6ejguy I was very surprised to see that they are developping a V4, V8, V12 at the same time ! As if a new engine type with zero off-the-shelf parts was not hard enough to bring to life.

[@NicksStuff]

Liked it. I would really like to see a small engine (Rotax 912 & co) comparison for ultralights

[@rumingjiang69]

Thanks for the very good comparison. What about Deltahawk?

[@rv6ejguy]

At about $80K, not sure how far it will go in the market. Not proven, no support network yet and can they even produce these in numbers? Took them 20 years to get it certified. Still years away from changing the landscape in my view.

[@predragbalorda]

I remember people mentioning difficulties in restarting a turbodiesel at high altitudes as being one of the drawbacks of raptor (debacle). Care to explain what is the issue and how austro ae330 and others deal with that?

[@rv6ejguy]

Diesels are compression ignition. If air density is halved at 18,000 feet, the effective compression ratio is halved so CR of 20 to 1 effectively becomes only 10 to 1 and won't cause the fuel to ignite. Combine this with low ambient temps and you have even more difficulty. Many early aero diesels were limited to 12,000 feet and most today still have a lower manifold pressure for flight to ensure they still lit at altitude. Loss of the turbo above 15.000 feet of so will also cause a flame out.

[@Mike-01234]

We drove our 2015 Ram 6.7 liter Cummins powered diesel with a 5th wheel over pikes peak stopped at the top of the summit 14000 feet high. We had lunch and walked around up there no problem starting the engine backup. It was cold so the glow plugs did turn on which was normal for temps below 60F. Maybe older diesel's worn out rings have issues never heard of the problem most RV people I see who tow a 5th wheel never told me of any issues they drive over Colorado all the time. Maybe the computer turns on the glow plugs wouldn't really know because it's always below 60F that high glow plugs heat up for 5-10 seconds anyway even down low in the winter.

[@PistonAvatarGuy]

@@Mike-01234 The SMA diesel was dropped by Cessna (partially) because they had problems with restarting it at altitude. The engine is air-cooled so it's going to be cooled as long as the aircraft is moving through the air, that's not so with a liquid-cooled truck engine that's parked. Trucks are not planes.

[@Mike-01234]

​@@PistonAvatarGuy I guess Continental has it figured out.

[@PistonAvatarGuy]

@@Mike-01234 Well, Thielert, which is the company that developed the diesel engines that Continental sells. It's all Chinese now, so whatever. Diesels still present problems in aircraft because they must maintain a minimum operating temperature and this requires engine power to be kept at a level which might be somewhat problematic in some situations (landing, taxiing).

[@bartofilms]

There are a couple marine outboard motors now which use spark but burn Diesel. Not sure, but I think they use a higher compression ratio than gasoline engines but not as high as the conventional Diesel.

[@rv6ejguy]

Some newer SI auto engines are at 13-14 CR now- almost as high as many diesels.

[@Mike-01234]

@@rv6ejguy Standard non Hight output 6.7L cummins is 19:1 static prior to turbo charging then add 38 PSI of boost to that. Never seen a gas engine that can come anywhere near that. They get 850 lbs of torque. the HO is 1075 lbs of TQ.

[@rv6ejguy]

@@Mike-01234 The Jesko 5L produces more torque on less than half that boost on pump gasoline and 1100 ft./lbs. on pump E85- gain with 1.7L less displacement and about half the boost.

[@Mike-01234]

@@rv6ejguy LOL $3 million dollar car revving to 8500 RPM compared to a stock ram 6.7 LT cummins diesel engine makes 850lbs of torque at 1700 RPM in a pickup that you can buy brand new in any city for $40k 2WD. Actually they sell a High output version that now puts out 1071 lbs of toque still get 20 mpg on the highway I get 14 in the city 7000lb truck. www.cumminshub.com/67.html That's completely stock with far less then 3 million dollars you can increase a 6.7 LT diesel up into 2000 of torque running on the same fuel you can buy at any pump in any city. Chevy, Ford also sell comparable engines not sure these can ever be adapted for aviation unless they are installed in a much larger aircraft. E85 isn't even sold at the pump in many states I never seen it here in Arizona. I do know that it burns at a faster rate so range is far less then diesel fuel. Here is a video of a 3000 HP 6.7LT diesel engine highly modified explode on a chassis dyno. kzbin.info/www/bejne/iWPdqHafpa2Nfbs

[@rv6ejguy]

@@Mike-01234 I don't consider price, application or fuel in these videos, just facts about specific hp and torque. I purposely found the most powerful diesel drag engine I could and compared it to an SI drag engine with 1/3rd of the displacement and 1/2 the boost pressure. The smaller SI engine spanked the diesel in the 1/4 mile. If we look at something more common- Ford Focus RS- running 91 pump gas. Scaled up to 6.7L to compare to the 6.7L Cummins, it would output 1020HP and 1020 lb./ft. of torque- still running half the boost.

[@captarmour]

love your videos. what about my fav legacy engine the continental 6 cylinder 360? i like because its smaller lighter pistons smoother 6 cylinders, crossflow heads. would love to see it developed to stand high boost and twice the power! what would that take?

[@umvhu]

Why do you say gasoline is lighter than diesel? I've not heard that before.

[@rv6ejguy]

Diesel fuel is around 7 pounds/ gallon, gasoline 6 pounds/ gallon.

[@ToyManFlyer1100]

Coz diesel has oil in it...Gas dont...

[@ZebulonAirRacing]

Could you add the UL 520 turbo to your comparison?

[@rv6ejguy]

Maybe in future, I can take a look at these engines if UL is willing to share info and photos with me.

[@gmcjetpilot]

This was great.... Obviously you go on what you know (data wise). My comment is extra weight of water cooling system not accounted for. The fuel burn on your mission chart does not include airspeed or MPG.... Some of these planes are faster. Obviously this involves airframe efficiency, including cooling drag. Engine cooling is both science and art. Often water cooled engines in planes designed air cooling are not always executed well and are draggy, more than the air cooled engine version of that plane. So an efficient engine is not as efficient if you are going slower. As more water cooled engines come into the market the art and science of water cooling in small tractor single enginel planes will be refined. The math and physics are known, eg P-51. The cooling design (water or air) has to be built into the airframe from the start. Last I predict Diesel (JET A) fuel will be around longer and more available in the distant future, vs AV GAS or MO GAS.... not in our lifetime but I see it happening.

[@rv6ejguy]

Just comparing in the same airframe at the same speed. Hypothetical exercise here to see how they all stack up.

[@gmcjetpilot]

@@rv6ejguy Great job... nice spreadsheets. Takes a lot of time to research. Thank you for this video. Price would a good data point, and availability of parts and maintenance is another dimension or factor. Thank you.

[@Mike-01234]

Too bad didn't include the rotax engines.

[@zain786ification]

How about the red engine ?

[@rv6ejguy]

It was too big and heavy to apply to most airframes plus cost is rumored to be something like $125K.

[@MAGApepe]

just dont get one of those diamond diesels with over sized pistons that needs a new engine

[@venusreena2532]

I wanted diesel ... still do

[@tinolino58]

Who belives Adept?

[@rv6ejguy]

We'll have to see. They are starting to ship engines now to US customers. It's a start.

[@robertrade]

@@rv6ejguy what's the website link for that adept 320T diesel aero engine? Love your videos!

[@rv6ejguy]

@@robertrade These are spark ignition engines. flyadept.co.za/engines/

[@tinolino58]

@@rv6ejguy it’s jun 2023: any real numbers from flying? Maybe they are in Oshkosh? Great videos!!!

[@rv6ejguy]

@@tinolino58 Adept never came through with their promised updates to me so I could do a follow up vid. I requested multiple times and received only one photo of an engine being installed on a Velocity. This was months ago now and nothing since then. IMO that doesn't look so good on them... The price has gone through the roof as of late. I don't expect a big following as a result. Too many years in development, too much money spent trying to certify (big mistake in my view) so now ROI demands charging a lot more for this engine. The death knell of so many new engine designs...

[@markspc1]

I am trying to stay awake, your monotone voice...

[@ianjon2248]

I think I'll call bull****. For example the best otto (normal car/plane) engine on wikipedia is the prius BSFC is 0.370 (en.wikipedia.org/wiki/Brake-specific_fuel_consumption) and yet these guys claim 0.33, the question that I'd ask is where did they get that data point as it would appear to be wrong, and if that data point is wrong all their data points are suspect. The thermal efficiency of any heat engine is limited by the delta T ie the difference in temperature between the environment and the max temperature produced. The reason that diesels get better fuel economy is simple physics, 1 the fuel has a higher calorific content and 2 the combustion temperatures are higher due to the higher compression. This engine is low compression and petrol (gasoline) powered so its really unlikely to stand a chance of actually really meeting those numbers assuming they mean lb/hpH.

[@rv6ejguy]

Data taken from dyno test provided by the manufacturer. We can only know how accurate this is when the engine is put in widespread service and we can observe the TAS vs. fuel flow in a known airframe. I my other videos I discuss the BSFC of SI vs. CI engines and we see the latest auro SI engines matching or exceeding comparable CI engines in this regard. The Otto cycle is considerably more efficient than the Diesel cycle. Once CRs are close, the SI engine can deliver superior BSFC figures at high load. The R3350 engine from the '40s had a BSFC figure of .37 with a sub 7 to 1 CR (turbo compound). The Conti 550 also gets around this figure LOP.

[@PistonAvatarGuy]

That's not the best BSFC for an Otto cycle engine, that's just the best one on that list. Toyota has since improved on that number (the engine in the Prius is now 41% efficient, not 36.4%), and the Prius engine is a mass production automotive engine which must conform to emissions standards all over the world, so it's limited to running at stoichiometric fuel mixtures. For decades, racing engines have been able to achieve BSFC numbers of around 0.34, as did the Continental Voyager engine used on the Rutan Voyager.

[@ianjon2248]

@@PistonAvatarGuy The best figures that I've seen for a prius is 40%, also most engines actually run leak of peak, not stoichiometric as this ensure fewer unburnt hydrocarbons. The prius gets a BSFC of about 0.347. The Adept 320 apparently beats Toyota with an efficiency of 41.9% without the multi-million dollar research budget. I would suspect that it's more likely that their method of calculating efficiency is flawed or inflated for other reasons. Diesels are naturally significantly more efficient due to fundamental laws of thermodynamics. Rather than simply spouting what appear to be ridiculous marketing claims it would be nice to see people put their brains into gear.

[@PistonAvatarGuy]

@@ianjon2248 The conventional version of Toyota's 2.0 liter Dynamic Force engine reaches 40% thermal efficiency, while the Atkinson cycle version of the engine (for hybrid models, like the Prius) reaches 41%. Modern automotive engines do not run LOP. Car companies stopped producing lean-burn engines in the '90s, as they could no longer meet emissions regulations (lean-burn engines produce too much NOx). Edit: The first gen Honda Insight used lean-burn tech until 2006. Diesels are only more efficient than gasoline engines when their compression ratio is significantly higher, but modern gasoline engines have been closing the gap. On KZbin: Diesel vs. Spark Ignition. Torque and HP by rv6ejguy Sorry, but you have no idea what you're talking about.

[@ianjon2248]

@@PistonAvatarGuy You're a goose, NoX production is generally a function of combustion temperature and pressure (See Haber-Boshe Process en.wikipedia.org/wiki/Haber_process) and while excess oxygen does force the reaction to the right it also improves fuel economy. Note that modern engines use combustion near the stoichiometric point to reduce NoX not to improve fuel consumption. So you can be even more efficient by emitting NoX with a lean burn. en.wikipedia.org/wiki/Lean-burn#Toyota_lean-burn_engines. Diesels have effective pressures of up to 23:1 which is much higher than petrol engines allowing higher combustion temperatures and hence higher efficiencies. Petrol engine compression is limited by the octane of the fuel to about 9:1 whereas diesel engines are not hence diesels can operates at higher efficiencies (which is why trucking companies use diesel engines as fuel is their biggest cost). So "closing the gap" is a silly comment as the efficiency of the engine is limited by underlying compression not by magic. Anyway the comment was that the efficiency figures being quoted are a "overly optimistic" however as they say "the fool and his money are easily parted" so you go an buy this very efficient engine. Meanwhile I'll invest in things that I think are supported by basic science and engineering principals.