Propane, sometimes referred to as liquefied petroleum gas (LPG), has become an increasingly popular fuel alternative for both gasoline and diesel engines. With propane prices often significantly lower than both gasoline and diesel, many vehicle owners are interested in whether their engines can be converted to run on this alternative fuel. So an important question arises: can a diesel engine run on propane?
In this comprehensive guide, as a professional diesel engine parts supplier, we’ll cover everything you need to know about running a diesel engine on propane.
How Diesel Engines Work
To understand the modifications needed for a propane conversion, we first need to review how diesel engines operate. Ignition and combustion work differently than in a gasoline engine.
The diesel cycle relies on heat and pressure inside the cylinder to ignite the fuel sprayed in by the fuel injector. No spark plugs generate a spark to ignite a diesel engine.
Instead, air is drawn into the cylinder and compressed by the rising piston. This causes the temperature in the cylinder to rise to over 1,000°F.
Then, just before the piston reaches the top of its travel, the fuel injector sprays a finely atomized diesel fuel mist into the hot, high-pressure air. The heat causes the diesel fuel to ignite spontaneously.
This ignition generates even more heat and rapidly increases the pressure further, pushing the piston down to produce power. The cycle then repeats, drawing in more air, compressing it, injecting more fuel, and combusting it.
So in summary:
- No spark plugs
- Relies on heat and pressure for auto-ignition
- Uses high pressure fuel injectors
Modifying a diesel to run on propane means completely changing this ignition and fuel delivery system while retaining the high compression ratio needed for diesel operation.
Can Propane be Used in a Diesel Engine?
Technically, yes propane can be used in a diesel engine. But it requires major modifications to the fuel system, ignition system, and engine management computer.
The high auto-ignition temperature of propane of 900°F means it won’t spontaneously ignite when sprayed into the hot, compressed air in the cylinder like diesel fuel does.
So the first challenge is figuring out how to ignite the propane. Some possibilities are:
- Add spark plugs – This allows igniting the propane with an electric spark. But now you need a reliable spark delivery system, ignition coils, and more.
- Premix propane/air – Mixing the propane and air before it enters the cylinder raises the mixture’s combustion temperature. But this reduces performance and makes metering the proper fuel ratio difficult.
- Dual fuel – Keep the standard diesel fuel system and inject a small amount of diesel to ignite a larger charge of propane. Complex to develop but avoids major engine modifications.
In addition, gaseous propane needs a completely different high pressure fuel delivery system compared to liquid diesel fuel. This typically means developing a custom fuel rail and injectors for propane service.
Finally, the engine management computer needs new calibrations and programming to account for the different combustion properties of propane and the new fuel control strategy.
As you can see, while possible in theory, converting a diesel to run on propane requires some complex changes!
Past Propane Diesel Conversion Attempts
Researchers, companies, and even fleets have tried converting diesel engines to run on propane over the years. One of the most promising attempts was done by IMPCO Technologies in 2009.
They spent $20 million on a conversion system for heavy-duty truck engines requiring:
- Modifying the cylinder head for spark plugs
- Machining the piston for clearance
- Adding an ignition system and propane fuel rail
Field testing showed over 85% lower emissions compared to diesel and 5 million miles of reliable operation in over 150 trucks.
Several other projects have looked into using propane and diesel in a dual fuel configuration. In this method, a small amount of diesel fuel, enough to trigger auto-ignition, is supplemented by a larger charge of propane.
This avoids the need to completely replace the stock diesel ignition and injection systems. And allows the engine to take advantage of propane’s higher octane rating for better efficiency.
Research is still ongoing but dual fuel propane-diesel could end up being the most straightforward conversion method.
Can a Diesel Generator Run on Propane?
Stationary diesel generators face less integration challenges compared to engines in vehicles. So converting generators to operate on propane using a basic spark ignition system is simpler.
Several dual fuel propane-diesel generator systems are already on the market from major brands like Generac. These systems retain the stock diesel fuel system for starting, shutdown, and as a backup. Then a secondary propane fuel system feeds propane for the majority of operation.
Switching generators to run primarily on propane can save over 50% in annual fuel costs in some cases. And by tuning the engine properly, the same peak power levels as with 100% diesel are achievable.
Most converted generator systems retain the stock diesel system as a backup fuel supply for reliability. And to lubricate injectors and fuel pumps that require diesel fuel for cooling and lubrication.
Propane Diesel Conversion Costs
Depending on the specific approach, propane conversions can run anywhere from $5,000 to $20,000. And perhaps double that for a full diesel program for a larger motor. Significant hardware and programming changes are needed in most cases for a complete swap to propane.
Using propane as a supplemental fuel in a dual fuel system costs much less with full conversion kits starting around $1,500. But performance gains are lower and you need to factor in ongoing propane fuel costs.
Generator conversions land somewhere in the middle price-wise but provide the largest potential return through lower fuel costs.
Keep in mind that attempting your own propane diesel conversion using cobbled together hardware risks damage to engines worth $10,000+, safety issues, and compliance problems. Professionally developed systems from companies like IMPCO, ATS, Generac, and others undergo extensive validation for durability, performance, and emissions.
The Bottom Line on Propane Converted Diesel Engines
- Modifying a stock diesel engine to run solely on propane requires significant changes to ignition systems, fuel systems, engine calibration, and likely some internal components.
- Most promising approaches use propane alongside diesel fuel in dual fuel configurations. This allows retaining the stock diesel ignition hardware while supplementing it with propane.
- Stationary diesel generators are the easiest application for propane conversion. And provide the fastest return on hardware investment through lower propane fuel costs.
- For now, vehicles like heavy duty diesel trucks are better off sticking with diesel fuel or opting for emergent eFuels which can use existing engine hardware.
The allure of cheaper, cleaner propane fuel will continue research into making diesel engine conversions more straightforward. But the complexity means it remains a niche solution today.
What do you think about using propane to fuel diesel engines? Have you heard of any other interesting alternative fuel conversion projects? Let me know in the comments! I’m always keeping an eye out for new engine technologies.