Report: Honda to Introduce Hybrid Fit in 2007 Using Insight Powertrain
EPA Launches Task Force to Review Boutique Fuels

A Lightweight, V-4, Two-Stroke Diesel for Aviation

DeltaHawk diesel engine.

DeltaHawk Engines, a small Wisconsin company, is developing a family of lightweight, V-4, two-stroke, turbo- and super-charged diesel engines for a variety of general aviation and non-aviation uses. The engines will run on Jet A (JP5) fuel, or #2 diesel where ambient temperatures are high enough to avoid gelling (above 20° F).

There are other diesel aviation engines—“aero-diesels”—available in the international market, but Deltahawk is poised to become the first US-based vendor.

Thielert Aircraft Engines GmbH (TAE) (Lichtenstein, Germany) builds the Centurion 1.7, for example, a 1.7-liter, 4-cylinder, 4-stroke, 4-valve, in-line diesel cycle engine with common rail direct injection. It can burn Jet A1 and Diesel (EN 590) in any mixture ratio.

(TAE has begun maintenance training in the US in anticipation of its bringing it to market.)

SMA (Bourges, France) offers an opposed-cylinder diesel cycle engine that burns Jet A fuel.

There are also several diesel aviation engines under development. US-based Teledyne Continental Motors began working on a two-stroke 4.7-liter, horizontally-opposed diesel cycle engine (TCM GAP) fueled by Jet A in 1997. Zoche in Munich, Germany is developing an air-cooled, radial two-stroke diesel with 4 cylinders per row. It features two stage charging (turbo- and super-charger), direct fuel injection and intercooling.

Interest in aero-diesels stretches back to the 1930s, with the introduction of several models of the Junker Jumo two-stroke, 6-cylinder, vertically-opposed engine. Given a variety of factors, general interest in the diesel cycle for aviation waned until recently.

With carbon dioxide issues and the cost and availability of fuel increasingly an issue for general and commercial aviation, the lower fuel consumption (and lower CO2 emissions of the diesel cycle is becoming increasingly attractive.

In 1998, the president of Lycoming, a leading manufacturer of general aviation engines, said that the time was right to develop and to market aero-diesels.

The wide availability of jet fuel makes diesel engines attractive as powerplants. Plus, the increased fuel efficiency fits well with aircraft engine design goals. With new lighter alloys, we can also see significant reductions in the dry weight of these engines, long known as efficient, but heavy

—Jim Koerner, Lycoming

(Koerner made those remarks during the announcement of a partnership with Detroit Diesel to develop such an engine. The engine, according to Andre Teissier-duCros, the publisher of DieselAir Newsletter, was sold to DaimlerChrysler which then abandoned it. )

A top view of the DeltaHawk, with a comparison to the footprint of the Lycoming IO-360. Click to enlarge.

The DeltaHawk engine. The DeltaHawk engine is an upright 90ª V-4, super- and turbo-charged, direct drive, liquid-cooled (glycol/water) two-stroke diesel with oil pump and external air-oil separator/sump.

The compact two-stroke design—which offers a higher power density than a four-stroke engine—results in a lower part count and fewer potential leakage points than the current 4-cylinder gasoline-powered aircraft engines. There is no camshaft or valve train, nor head gasket or head bolts.

Fuel consumption comparison. Click to enlarge.

It comes in 160 hp (119 kW) and 200 hp (149 kW) models and weighs about 327 pounds. DeltaHawk says that its engine delivers 20–30% more range per gallon, and a BSFC (brake specific fuel consumption) of .37 lb/hp/hr versus current avgas-powered aviation engine book BSFC of .59 lb/hp/hr at 75% and above.

The fuel issue. Conventionally, aviation fuels are classified into two general groups: aviation gasolines for reciprocating piston engines, and kerosene-type aviation turbine fuels for use in turbo-propeller and turbo-jet engines. Those turbine fuels—of which Jet A is a member—can also be used in a compression ignition (diesel) reciprocating engine.

The rising cost of fuel is one of the most critical issues faced by both commercial and general aviation. (Emissions are another.)

Thus, one of the next major technology challenges for the entire airline industry is the development of alternative fuels that are cleaner-burning, and lower in cost than the petroleum-based fuels, according to Giovanni Bisignani, Director General & CEO of the International Air Transport Association (IATA).

While synthetic fuels (e.g., Fischer-Tropsch fuels) are of great interest for commercial and military aviation, blending biodiesel with the existing kerosene-based fuels is a route that many researchers are exploring.

One of the main issues with biodiesel in aviation is the gelling at low-temperature.

As one approach to resolving that issue, researchers at Purdue developed a 40% biodiesel, 60% Jet A blend that meets ASTM D-1655 (Jet A) fuel specifications for cold temperature behavior (freezing at a temperature not higher than -40° C).



Sid Hoffman

The article above says the DeltaHawk engine is an "upright" engine, but it's actually available in 3 orientations. Upright (V-shaped), inverted (^-shaped), or vertical, such as for use in small helicopters. That reduction in part count also results in a far lower total cost of ownership since there's no spark plugs to replace, no head gaskets to inspect, no cams to check for wear, and so on. It's really the future of General Aviation engines.

Separately, because it's turbo-normalized, it can maintain full power to somewhere between 15,000 and 20,000 feet. It's mission weight is comparable to the Lycoming 160-200hp naturally aspirated engines, which of course make substantially less power as you rise in elevation. The DeltaHawk not only can use less fuel at cruise, it will reach cruising altitude far more quickly by virtue of being turbo-normalized. The more percentage of time you spend at cruise altitude, the lower your total fuel consumption will be.


I've been watching DeltaHawk for years.  They've got quite a product, though I think Zoche might have a market advantage if they can ever get there.

I note from DeltaHawk's website that they have started the certification process.  Certification will allow the engine to be used on non-experimental aircraft.  I hope they breeze through.


If the maintenance costs are lower and with the expected gains in fuel efficiency I might just go out and get my light sport license when these engines are available.

Sid Hoffman

Actually a light sport license will only certify you for very small aircraft with a maximum weight of 1320 pounds and maximum speed of 138mph. Even the least powerful DeltaHawk would propel such a light aircraft to well over 200mph, so it's not really an option. I believe most aircraft of that category are designed around the naturally aspirated 100hp Rotax air-cooled gasoline engine.

The DH would make a nice replacement for Cessna 172's however, since most all of those came with 160-200hp naturally aspirated gasoline engines. In fact on DH's site you'll see they actually have a test aircraft with a working DH installed in a Cessna 172. The only real problem with turbo engines honestly is that it makes it a lot easier to pass Vne since you don't lose power as you climb. It's kind of better to have an aircraft that's actually designed for a turbo-normalized engine, like perhaps some of the Cessna 182 skyhawks for example, as a candidate for the 200hp version.

Eventually, leaded gas will be banned and there will be a TON of Cessnas, Pipers, and other aircraft looking for new engines that run on either 87-91 octane mogas or Jet-A.

allen zheng

Lets see if they can push fuel->mechanical energy efficiency from ~30-33% to ~41-42% using pilot injection technology. Afterwards, adding thermoelectric elements in the post treatment (if any, and most likely yes due to Euro Union enission standards) pipe walls to make electricity for powering the supercharger/pumps/other mechanical-electric loads. That might push the overall efficiency to ~55-58%, if not higher due to better materials/technology/use of more thermoelectric elements. Additionally, The use of heat-electric recovry could run a more powerfull supercharger to enable more power at higher altitudes, thus ensuring greater cruise range and max speed (due to less drag on aircraft). On the comparison chart, the line for 11,500 ft. could be over 50 Kn/pg for 120 Knts airspeed.

tom deplume

I've been reading comments about once the fossil fuel is gone aviation will be a thing of the past. Show me a car that gets 45 mpg at 100 mph.


The energy density of petroleum products is essential to aviation as we know it. But running out of gas will not directly bring the jet age to an end. If I understand the numbers correctly, aviation uses only account for around 10% of our oil consumption. Maritime uses are harder to pick out of the numbers I found, but likely do not exceed aviation uses, and are probably much smaller.

See: (Assuming that the "Jet Fuel Total" and "Aviation Gasoline" categories were aeronautical uses, and that "Residual Fuel Oil" plus some fraction of "Distillate Fuel Oil" -- which usually stands for diesel -- were for heavy marine uses. Some small fraction of gasoline probably goes to small craft marine use, but I basically ignore that segment.)

In a long-term worst-case scenario, where substantial quantities of oil are no longer pumped from the ground, it would be well within our capabilities to replace all aviation fuels with alcohol, biodiesel and Fischer-Tropsch products. We already have the technology to do this, but conventional petroleum remains cheaper or more economically rational, in the short term at least (think of all the installed infrastructure).

If renewable liquid fuels could not be made in the same total quantities that conventional fuels are currently made (for sea, air and ground uses), applications for which there are no good substitutes (air and sea) would bid the most and win the allocations needed to keep moving. Ground users would then have incentive to economize on liquid fuels very highly (small, efficient cars and hybrids), or switch to alternatives entirely (NG if available, batteries, fuel cells, overhead wires from trains and buses, etc.). The point is, there is every reason to expect that enough non-petroleum liquid fuels can be produced to satisfy users who have no clear substitute. Moving to such a state would be a huge project, and most of what we are discussing in this forum are the first steps on that path.

Regarding the present topic more specifically: Aviation gasoline, of the sort used in small planes, is currently a very tiny fraction of total aviation petroleum consumption. The total GHG difference that replacing every Cessna 172 gasoline engine with a diesel will be very modest. Smog and PM exhaust are much smaller concerns either way, as most of this fuel will be burned far away from populated areas. The main attraction in switching light props to diesel is simply the ability to fill up using the same fuel infrastructure that big jets use. Airports would have to stock up on one less fuel, which would save a good deal of overhead.

Furthermore, aviation gasoline is one of the very few remaining uses of tetraethyl lead -- the typical grade of avgas, 100LL, stands for "100 octane, low-lead." Cutting that out of the environment would be nice, as heavy metals are very persistant and tend to bioaccumulate, making them nastier than the average form of pollution.

Finally, Europe taxes avgas to an absurd degree (okay, that's a bit subjective). But the fact remains that Jet A fuel is several dollars per gallon cheaper over there. It also tends to be a bit cheaper over here too, but only by a little. Plus, high-grade road diesel (which most of these aviation diesels can burn) is also fairly affordable and available. An engine that burns much cheaper fuel, and does so more efficiently, is a natural thing in such a market, if reliability, size and weight can be controlled -- which they now can be, using modern materials.


tom deplume, my Insight averaged 50.1mpg maintaining 90mph thru the Shenandoah mountain range in Virginia.

And recently 52.3mpg maintaining 80+mph from Charleston WV, thru Virginia, and to Winston-Salem (I didn't feel like chancing the 90mph again :P ) while loaded over it's max weight rating with luggage.

So I'd be willing to try for 45mpg or better @ 100mpg if I weren't afraid of the police ^_^.

Roger Pham

Hi Allen Zheng,
Research on Thermoelectric energy recovery has shown practically ~12% thermal efficiency from the typical heat from engine exhaust. But, exhaust heat represents only 30% of total heat value from fuel combustion. Multiply 0.3 by 0.12 = 0.036, or 3.5% efficiency gain in total engine thermal efficiency. For an Otto-cycle engine with efficiency ~30-40%, this only represents a 10% gain in efficiency...but at what cost? Installing heat exchangers for hot and cold junctions are cumbersome for a vehicular application, and the thermoelectric material currently used can be quite expensive. This may potentially be a good idea but still in research stage, with uncertainties regarding cost-effectiveness, portability, and reliability. Thanks for many informative ideas.
Roger Pham

Lance Funston

Fuel gelling at 20 degrees? I think that must be an awfully common problem in aviation... as in flying in any winter weather or over 10,000 ft.

Giridhar Raju N M

Hi people,

I have been going through this page from quite recently. But I have a doubt.

We all know that two stroke diesels are very efficient & their use in Aero Applications has again proved this. But I dont Understand Why Two Stroke Diesel Engines Are not being used as widely for Road transport. As far as i could trace, i could not see any major automotive Company using a two Stroke Diesel for their passenger Car programme.

& the fact being THAT if even half the reaserch that goes to Four Stroke Diesels go into Two stroke Diesels we could definitely get better Engines.

Any Body Hearing.!!!!


Two stroke diesel for cars:

Unfortunately this light and efficient engine could not comply with exhaust emission regulation. When piston uncovers exhaust ports, outgoing rush of exhaust blows off lube oil accumulated in exhaust ports during piston’s up and down stroke. Fumes of semi-burned oil in exhaust are bad for itself, and in addition they plug in no time any exhaust aftertreatment filter, almost universally fit to modern transportation diesels. Blow-of from intake ports are much smaller (it burns mostly when fuel is combusted), but still is substantial. This is not an issue with aviation engines.

Rafael Seidl

Giridhar -

there have actually been many attempts to develop two-stroke diesel engines for automotiva applications, e.g. by Yamaha, Daihatsu and AVL in the 1990s. These 2 and 3 cylinder engines all featured approx. 1 liter total displacement and delivered 33 to 47kW nominal power. All used a regular oil sump, hydrodynamic bearings, inlet slits, exhaust valves, straight-through scavenging and a mechanically powered external scavenging pump. In addition, two of the designs featured a turbocharger.

The main benefits relative to a four-stroke engine with comparable power rating were shorter package, higher low-end torque (permitting more favorable gear ratios) and having the camshafts double as compensation shafts for first-order imbalances.

The main problems identified were:
- high thermal and mechanical load on the crank-slider mechanism, piston rings and piston liner (limiting feasible compression ratio)
- increased fuel consumption
- high oil consumption due to inlet slits
- relatively high PM and NOx emissions
- high cost (since crankcase scavenging was not used)

A NZ company, , has come up with a two-stroke design in which the traditional crank-slider four bar linkage is replaced with a pivot-slider. This introduces the possibility of internal water cooling of the piston crown, elimination of piston slap and oil delivery directly to the seal (claim: factor 10x less oil consumption). The engine uses reverse flow scavenging via the crankcase, the bearings are sealed roller types (loud, tricky for large inline cylinder counts). In addition to gasoline, they claim the basic concept is also suitable for hydrogen and diesel. However, I suspect it would be difficult to achieve high compression ratios.

A US company, , has brought a German design for an opposed-piston, opposed-cylinder (OPOC) two-stroke diesel engine with HCCI combustion to market. It is not possible to use regular DICI injectors for opposed-piston designs. The turbocharger features an electric assist motor to facilitate scavenging at low RPM. The in-cylinder pressure must always be kept above crankcase pressure because the inner connrods support their pistons via a sliding arc segment rather than a full wrist pin - this reduces lateral forces against the thermally loaded piston wall near exhaust slits. Hydrodynamic bearings and a dry sump are used. Several variants of the design are currently undergoing testing.

See also:


Little by little, they are getting closer to what I have been promoting for years; a twin cyclinder, opposed air-cooled, 2-cycle, biodiesel, lubicated with Castor oil.

It would be directly connected to nothing but a generator. Only run when the drive battery needed recharging and then at the most efficient speed.

Want to see the whole ball of wax? Search google for: William Lucas Jones Hybrid. You'll get about two pages, most all duplications. Some later ones indicate some improvements by Mitsubshi and Toshiba.

Don Arnold

Allen Zheng: I have to agree: Aviation will shrink to a small number of conventional airliners operating at Concorde plus prices. Little Cessnas? It already takes hard work and persistence to get any utility out of a privately flown lightplane, and the cost of alternative fuels will restrict piston powered general aviation to novelty/demo flights. The people who currently fly old WWII fighters might still be able to afford it. The FAA will balk at accomodating the last few hundred who can afford it. The investors currently in the new VLJ segment might recover their investment, but what lies beyond? Me, I'm thinking about my third experimental plane, an electric motorglider. Those who follow model airplanes know about the astounding growth of model e-flight with the adoption of lithium-polymer batteries. The power density is about 3 or 4 times better than Ni-Mh. It must be cost that keeps them out of hybrids. Discharge rates improve by the month it seems. At some point the cost of li-po will come down, the cost of alternative liquid fuels will go up, and you'll see electric planes charging up on 30c/kwh juice and taking off on occasional pleasure flights. Perhaps improved thermal imaging with electrostatic sensors will combine with onboard supercomputing power to make long distance thermal flight quite reliable. The sun puts plenty of energy into atmospheric turbulence everyday. If you could see the updrafts, you can go hundreds of miles for no energy, you just need the initial charge to get up there. Don

Marc Lacoste

Thielert made the only realistic engine, IMO: it's a mercedes CDI car engine, they also made a 4.0L V8. Manufacturers need to produce several hundreds of thousands of those to be competitive, and I'm afraid that for the small market of general aviation, car engines are the only way to go. But I think the JUMO 223 is one of the greatest enginering achievements.

Roger Pham

What lies beyond [in post-petroleum era] Mr. Don Arnold, will be that commercial Jet aviation will continue to thrive, as before. This will be courtesy of liquid methane (from biomass gasification) or liquid hydrogen (from renewable solar and wind energy). These Jetplanes will have their jet engines adapted to burn these cryogenic fuels from large insulated tanks. And who knows, the combined-cycle SCRAM Jet hypersonic planes running on liquid H2 will make a trip from NYC to Tokyo in under two hours. Somedays, H2 will be produced from solar energy at the cost comparable to kerosene at $2.50/gallon, or equivalent to the price of petroleum paid today. Likewise for renewable methane.

Noel Loveys

I really like the look of the Zoche two cylinder diesel engine.
In the past the world of amateur enterprise has given such things a digital television and even a lot of the procedures used on the internet.
I would like to see that same use be put forward in an engine like the Zoche. Countless hours of flight use should help work out any bugs and accelerate the production of a certified engine. It would allow the world to see the engine and would reduce the cost of certification for Zoche.... Everybody wins.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)