Experimental Diesel Aircraft Engines: The Future of Efficiency

Flying a plane costs money. A big part of that cost comes from fuel. For years, pilots have burned avgas in their engines, watching their fuel gauges drop and their wallets empty. 

But something is changing in the world of general aviation. Engineers are building and testing experimental diesel aircraft engines that burn less fuel and cost less to operate. 

According to recent industry analysis, diesel aircraft engines represent a potential revolution in how we power small planes. These new engines run on jet fuel instead of avgas, and they use less of it. The question isn't if diesel engines work in planes anymore. 

The question is how soon they'll become the normal choice for pilots everywhere.

This post goes into how these engines work and why they matter for pilots who want to save money.

Key Takeaways

Experimental diesel aircraft engines are piston engines that burn diesel fuel or jet fuel instead of avgas. They offer better fuel efficiency, lower operating costs, and reduced emissions compared to traditional aviation gasoline engines. These engines use compression ignition technology similar to car diesel engines but are designed specifically for aircraft use. Several companies are now producing certified and experimental diesel engines ranging from 100 hp to 350 hp for general aviation aircraft.

How Do Airplane Engines Work?

Most small planes use a piston engine to create power. The engine works like the one in your car, but it's built for flying. Here's how it happens.

Air and fuel mix together inside metal cylinders. A piston moves up and down inside each cylinder. When the piston moves down, it sucks in the air and fuel mixture. When it moves up, it squeezes everything tight. Then a spark plug fires, and the mixture explodes. This explosion pushes the piston back down with force.

The pistons connect to a crankshaft. When the pistons move up and down, they turn the crankshaft. The crankshaft connects to the propeller. As the crankshaft spins, the propeller spins too. The spinning propeller pulls the plane through the air.

Here's what makes airplane engines different from car engines:

• They run at high rpm for long periods without stopping
• They need to work well at different altitudes where air is thin
• They must be extremely reliable because you can't pull over in the sky
• They produce power measured in hp (horsepower)

Most small aircraft engines have four or six cylinders. A typical training plane might have a 180 hp engine. Larger planes might have engines with 300 hp or more. The engine turns the propeller at about 2,300 to 2,700 rpm during flight.

Traditional airplane engines burn avgas, which is a special type of gasoline made for aviation. This fuel costs more than regular gas you put in your car. It also costs more than diesel or jet fuel. That's one reason people are looking at diesel engines for planes.

What Is a Diesel Engine?

A diesel engine works differently than a gasoline engine. The main difference is how the fuel burns. Gasoline engines use spark plugs to ignite the fuel. Diesel engines don't need spark plugs at all.

Here's how a diesel engine creates power. The piston moves up and squeezes the air inside the cylinder. When air gets squeezed really tight, it gets hot. The air gets so hot that it can ignite fuel all by itself. At just the right moment, the engine sprays diesel fuel into that super-hot air. The fuel ignites immediately and explodes. This explosion pushes the piston down, creating power.

This process is called compression ignition. The engine compresses the air so much that it creates enough heat to burn the fuel. No spark needed.

Diesel engines have some advantages:

• They burn fuel more efficiently than gasoline engines
• They use less fuel to make the same amount of power
• They can run on different types of fuel, including jet fuel
• They last longer because they're built stronger

Modern diesel engines use injection systems that spray fuel at very high pressure. Some use common rail systems that keep fuel ready to spray at exactly the right moment. Many new diesel engines also use FADEC (Full Authority Digital Engine Control). This is a computer that controls the engine automatically. It adjusts the fuel and air mixture to get the best performance.

The computer also manages fuel consumption. It makes sure the engine burns only the fuel it needs. This saves money and helps the engine run cleaner. Diesel engines in planes use these same technologies to work efficiently at high altitudes.

Why Are Experts Testing Diesel Engines for Aircraft?

The debate about diesel engines in aviation has been going on for years. Now engineers have good reasons to keep testing them.

Cost is the biggest reason. Avgas costs a lot of money. In many places, it costs $6 to $8 per gallon. Jet fuel and diesel cost less. They also cost about the same everywhere you go. When you can burn cheaper fuel, every hour you fly costs less money.

Availability is another reason. Not every airport sells avgas. But almost every airport has jet fuel. If your plane can burn jet fuel, you can refuel at more places. This gives you more options for planning flights.

Environmental concerns matter too. Avgas contains lead, which is bad for the environment and for people. Diesel and jet fuel don't have lead. They burn cleaner. As rules get stricter about pollution, diesel engines look better and better.

Aero engineers also like how efficient diesel engines are. These engines can:

• Burn 30-40% less fuel than traditional engines
• Maintain power at high altitudes better
• Run longer between overhauls
• Work with existing jet fuel infrastructure

The technology keeps getting better. Early diesel airplane engines were heavy and unreliable. New ones are lighter and work well. Companies have spent millions of dollars developing engines that are safe and efficient.

Pilots care about reliability. Diesel engines have fewer parts that can fail. They don't have magnetos or spark plugs that wear out. The FADEC system monitors everything and adjusts the engine automatically. This makes flying simpler and safer.

Some experimental aircraft builders want engines that cost less to maintain. Understanding aircraft engine costs helps them make better choices. Diesel engines often need less maintenance over their lifetime.

Are Experimental Diesel Aircraft Engines the Key to Better Efficiency?

The short answer is yes. These engines deliver real improvements in fuel economy and operating costs. Here’s a look at the details.

The Current State of Diesel Aviation

Several manufacturers now make aircraft diesel engines that pilots can buy and install. These aren't just prototypes anymore. They're real engines flying in real planes.

Austro Engine GmbH makes some of the most popular diesel engines for small planes. Their engines power many Diamond Aircraft models. Diamond has been using diesel engines for years. They've proven these engines work reliably in everyday flying.

DeltaHawk Engines in the United States builds a different type of diesel aircraft engine. Their engine uses a unique two-cylinder design. It's lighter than many competing engines. The company has been testing and improving this engine for several years.

Here are some key players in the diesel aviation market:

• Austro Engine (part of Diamond Aircraft Industries)
• Deltahawk (based in Wisconsin)
• SMA Engines (French manufacturer)
• RED Aircraft GmbH (German company)
• Diesel Air Limited (Australian developer)

Each company takes a different approach to engine design. Some adapt car engines for aviation use. Others build engines from scratch specifically for planes.

Power Options for Different Planes

Diesel engines now come in many power levels. You can find an engine available for almost any size plane.

Light-sport aircraft can use smaller engines:

• 100 hp engines work well for ultralight and sport planes
• 120 hp versions provide more power for two-seat aircraft
• These engines weigh less and cost less than larger models

Mid-range engines serve popular training and personal planes:

• 135 hp to 160 hp engines replace common Lycoming and Continental models
• 180 hp versions fit many four-seat aircraft
• 200 hp engines provide good performance for traveling planes

Larger engines power bigger aircraft:

• 230 hp to 300 hp engines suit light twin aircraft and larger singles
• 350 hp versions can replace traditional high-power engines
• These engines often use turbo charging to maintain power at altitude

The Gemini 100 from Deltahawk produces 180 hp. It's designed as an engine replacement for traditional Lycoming engines. Many builders like this option because it fits in the same space as the engine it replaces.

Austro Engine makes several popular models. Their AE300 produces 170 hp and is EASA certified. This means it meets strict European safety standards. Many new aircraft come with this engine from the factory.

Technology That Makes Them Work

Modern diesel aero engines use advanced technology. These aren't your grandfather's tractor engines.

Direct injection systems spray fuel right into the cylinders. The fuel spray happens at very high pressure, sometimes over 2,000 pounds per square inch. This high pressure breaks the fuel into tiny droplets. The small droplets burn more completely and create more power.

A 4 stroke 4 cylinder diesel engine works like a traditional airplane engine. It has four pistons moving in four separate cylinders. Each piston completes four steps: intake, compression, power, and exhaust. This familiar layout makes it easier for mechanics to understand and maintain.

FADEC systems control everything automatically:

• They adjust fuel injection timing based on altitude and temperature
• They monitor engine control parameters hundreds of times per second
• They optimize the mixture for best fuel economy
• They protect the engine from damage by limiting temperatures and pressures

A 4 cylinder diesel with FADEC gives pilots a single lever to control power. Push the lever forward, and the engine makes more power. Pull it back, and power decreases. The FADEC does all the mixing and adjusting automatically. No more fidgeting with mixture controls or worrying about fouling spark plugs.

The turbo diesel design helps engines maintain power at high altitude. As you climb higher, the air gets thinner. A naturally aspirated engine loses power. But a turbo charged engine uses exhaust gases to spin a compressor. The compressor pushes more air into the cylinders. This lets the engine keep making power even when the outside air is thin.

Fuel Options and Efficiency

One of the best things about diesel aero diesel engines is fuel flexibility. These engines can burn multiple types of fuel.

Jet fuel (also called Jet A-1 or Jet A1) is the most common choice:

• Available at almost every airport worldwide
• Costs less than avgas in most places
• Doesn't contain lead
• Stores longer without degrading

Diesel fuel works in these engines too. If you can't find jet fuel, you can use regular diesel from a truck stop. This flexibility gives you more options when you're traveling to remote areas.

The fuel burn improvements are significant. A traditional Lycoming or Continental engine might burn 10 gallons per hour. A comparable diesel engine might burn only 6 to 7 gallons per hour. Over hundreds of hours of flying, this adds up to thousands of dollars saved.

Let's compare a petrol engine to a diesel in a typical four-seat plane:

Traditional Gasoline Engine:

• Burns 9 gallons per hour
• Avgas costs $7 per gallon
• Hourly fuel cost: $63
• Annual cost (100 hours): $6,300

Diesel Engine:

• Burns 6 gallons per hour
• Jet fuel costs $5 per gallon
• Hourly fuel cost: $30
• Annual cost (100 hours): $3,000

The diesel saves $3,300 per year in this scenario. Over ten years, that's $33,000 in fuel savings alone.

Lower fuel consumption also means you can fly farther on a tank. A plane with a 50-gallon fuel tank can fly about 5.5 hours on gasoline. The same plane with a diesel engine can fly about 8 hours. That's a huge increase in range.

Design Variations

Manufacturers use different designs to solve the same problem. Each design has pros and cons.

Horizontally opposed engines look like traditional airplane engines. They have cylinders on each side of the crankshaft. The pistons move toward each other. This design fits easily in standard engine mounts. It's familiar to mechanics. Most diesel airplane engines use this layout because it works well and fits in existing planes.

The radial diesel engine is less common. In a radial design, the cylinders point outward from a central crankshaft like spokes on a wheel. This design is compact and efficient, but it's harder to cool properly. Few companies make radial diesel engines for aircraft.

Some engines are based on a car engine. The Austro Engine started as a Mercedes diesel engine. Engineers modified it for aviation use. They changed the valve system, added a different cooling system, and installed aviation-specific engine control systems. Using an existing car engine as a starting point saves development time and money.

Prototype engines often test new ideas. Red Aircraft GmbH developed a V6 engine that produced 500 hp. The engine used a two-stroke diesel design. Two-stroke engines fire every time the piston goes down, not every other time. This makes them more powerful for their size. However, two-stroke designs can be less reliable and burn more oil.

Real-World Applications

Diesel powered planes are flying right now. They're not some future technology. You can buy one today.

Diamond Aircraft sells several models with diesel engines:

• The DA40 NG uses a 170 hp diesel engine
• The DA42 twin uses two diesel engines
• The DA62 uses two 180 hp diesel engines

These planes fly in flight schools around the world. Students learn to fly in diesel aircraft every day. The engines have proven they can handle the hard use of training operations.

Small aircraft builders also choose diesel engines. Experimental aircraft builders can install any engine they want. Many builders who want to replace traditional engines pick diesel options for the fuel savings.

The aviation market is watching these developments closely. General aviation aircraft owners want engines that cost less to operate. They want to fly to more places without worrying about fuel availability. Diesel engines solve both problems.

Superior Air Parts and other companies make parts for diesel aviation engines. As more planes use diesel engines, more support businesses emerge. This creates a better supply chain for parts and service.

Performance Characteristics

Let's talk about real performance numbers. How do these engines actually perform?

A typical hp diesel engine running at 2300 rpm produces steady, smooth power. The engine doesn't vibrate as much as a gasoline engine. This makes the plane quieter and more comfortable.

The engine produces power at lower rpm than gasoline engines. A gasoline engine might cruise at 2,500 rpm. A diesel engine might cruise at 2,000 rpm. Lower rpm means less wear on parts. It also means the engine lasts longer between overhauls.

Here are some specific examples:

Austro AE300:

• Power: 168 hp at 2300 rpm
• Weight: 394 pounds
• Fuel burn: 4.5 gallons per hour at cruise
• TBO: 2,400 hours

DeltaHawk DHK180:

• Power: 180 hp
• Weight: 385 pounds
• Fuel burn: 5 gallons per hour at cruise
• TBO: 2,000 hours (estimated)

Compare this to a traditional Lycoming O-360:

• Power: 180 hp
• Weight: 325 pounds
• Fuel burn: 8 gallons per hour at cruise
• TBO: 2,000 hours

The diesel engine weighs more, but it burns much less fuel. The extra weight pays for itself in fuel savings on longer flights.

Certification and Regulations

EASA (the European Aviation Safety Agency) has certified several diesel engines. EASA certified engines meet strict safety and reliability standards. They can be installed in production aircraft.

In the United States, the FAA has been slower to certify diesel engines. However, experimental aircraft builders don't need certified engines. They can install prototype engines or new engine designs in their homebuilt planes.

This freedom has helped aircraft engine development move faster in the experimental category. Builders test new ideas and report their experiences. This real-world testing helps manufacturers improve their designs.

The Economics

Money drives many decisions in aviation. Let's break down the real costs.

A new engine costs money upfront. A diesel aircraft diesel engine might cost $40,000 to $70,000. A comparable gasoline engine costs $30,000 to $50,000. The diesel costs more initially.

But look at operating costs over time:

10-Year Ownership (1,000 hours):

Gasoline Engine:

• Initial cost: $40,000
• Fuel (9 gph × $7): $63,000
• Maintenance: $15,000
• Total: $118,000

Diesel Engine:

• Initial cost: $60,000
• Fuel (6 gph × $5): $30,000
• Maintenance: $12,000
• Total: $102,000

The diesel engine saves $16,000 over 10 years, even though it costs more upfront. Fly more hours, and the savings increase. Understanding engine overhaul options helps you make smart decisions about engine investment.

Market Growth and Future Trends

A number of companies are investing in diesel aviation technology. The general aviation market is slowly accepting these engines.

Propulsion systems for general aviation aircraft are changing. As gasoline becomes harder to find and more expensive, diesel makes more sense. Some countries in Europe already have limited avgas availability. Pilots there need alternatives.

New designs keep improving the technology. Engine features that were impossible ten years ago are now standard. FADEC systems get smarter. Engines get lighter. Fuel system designs get more efficient.

Aircraft like the Diamond DA62 show what's possible. This twin-engine plane flies on diesel power. It can cruise at 180 knots while burning less fuel than older single-engine planes.

The future looks promising for diesel aviation. More manufacturers are entering the market. More planes come with diesel engines as standard equipment. More pilots are choosing diesel because the economics make sense.

Challenges Remaining

Diesel aviation engines still face some challenges. They're heavier than gasoline engines. The extra weight affects performance and payload.

Cold weather starting can be harder. Diesel fuel gets thick when it's cold. Some engines need preheating systems in winter climates.

The fuel system is more complex than gasoline systems. High-pressure pumps and injectors need precise maintenance. Not every mechanic knows how to work on diesel airplane engines yet.

Parts availability can be an issue. If something breaks, you might wait for parts to ship from Europe. This downtime costs money and frustration.

But these challenges are getting smaller. As more planes use diesel engines, more mechanics learn to work on them. Parts distribution improves. Cold-weather technology gets better.

Conclusion

Experimental diesel aircraft engines are changing how we think about powering small planes. They burn less fuel, cost less to operate, and give pilots more options for where they can refuel. The technology has matured from experimental prototypes to reliable engines flying thousands of hours each year.

The economics are convincing. Lower fuel consumption means real money saved on every flight. The ability to burn jet fuel instead of expensive avgas opens up new destinations and simplifies flight planning. As more manufacturers enter the market and more pilots gain experience with these engines, diesel power will become more common in general aviation.

For pilots and aircraft owners looking for current information about aviation technology and aircraft for sale, Flying411 provides resources to help you make informed decisions about your flying future.

Frequently Asked Questions

How long do diesel aircraft engines last before needing overhaul?

Most diesel aircraft engines have a TBO (Time Between Overhaul) of 2,000 to 2,400 hours. This is similar to or slightly better than traditional gasoline engines. The actual lifespan depends on how well you maintain the engine and how you operate it. Proper oil changes, regular inspections, and following manufacturer guidelines help engines reach or exceed their TBO limits.

Can diesel aircraft engines run on regular automotive diesel fuel?

Yes, most diesel aircraft engines can run on automotive diesel fuel in addition to jet fuel. However, manufacturers typically recommend using jet fuel because it has better cold-weather properties and more consistent quality standards. Automotive diesel works fine in warmer weather and emergency situations. Always check your specific engine's manual for approved fuel types.

Are diesel aircraft engines harder to maintain than gasoline engines?

Diesel aircraft engines require different maintenance, but not necessarily more maintenance. They don't have spark plugs or magnetos to replace, which simplifies some tasks. However, fuel injection systems need attention, and high-pressure fuel pumps require specific care. Finding mechanics experienced with diesel aircraft engines can be challenging in some areas, but this is improving as more planes use these engines.

Do diesel aircraft engines work well at high altitudes?

Turbocharged diesel aircraft engines actually perform very well at high altitudes. The turbocharger compensates for thin air by compressing more air into the cylinders. This allows the engine to maintain power at altitudes where naturally aspirated engines lose performance. Many diesel aircraft engines can cruise efficiently at 10,000 to 15,000 feet with minimal power loss.

What happens if I can't find jet fuel at a remote airport?

Diesel aircraft engines give you flexibility in this situation. You can use automotive diesel fuel from a nearby truck stop if jet fuel isn't available. Some pilots carry fuel filters and hand pumps for emergency refueling. This fuel flexibility is one of the main advantages of diesel engines. Always carry documentation showing your engine is approved for multiple fuel types.