What can be easier or simpler than adding LPG to a diesel engine? Isn't it as simple as tossing a 20 lb barbeque cylinder in the back of a pickup truck and running a hose from the cylinder's regulator to the engine?

Yes, it can be that simple BUT that it can also be a shortcut to destroying your engine or to killing yourself or others around you. From a safety aspect, most people attempting this type of fuel system are often oblivious to the requirements of the gas code (NFPA 58 and CSA B149.5), which regulates the use of propane fuel in automobiles. These regulations were developed over many years through industry experience and responses to accidents and are akin to the National Electric Code for home wiring. You know that, if you cut corners with wiring, it's only a matter of time before your house burns down or someone gets electrocuted. Cutting corners with home-brewed propane or natural gas conversions can be just as risky.

On a BTU basis, propane must be less than 65% of the price of diesel to save money on fuel costs. CNG is typically priced in terms of GGE (Gasoline Gallon Equivalent) so its price must be less than 90% of the price of diesel to save money on fuel costs. Conversely, you can multiply the price of propane by 1.541 to get its Diesel Gallon Equivalent (DGE) price. Similarly, you can multiply the price of CNG by 1.115 to get its DGE price. Because the retail DGE price of propane is usually more than the price of diesel, diesel-propane systems are often used to boost power rather than to save money on fuel. CNG, on the other hand, is usually much cheaper than diesel (on a DGE basis) so it can potentially significantly reduce overall fuel costs. Since CNG and LPG burn so much cleaner than diesel, the regen cycle times on post-2007 vehicles should also reduced with an additional boost in savings. In addition, CNG has a higher octane number than propane so it can be used in higher relative amounts than propane. However, because CNG is a supplemental fuel, power gains can potentially be similar to those of propane.

Detonation (knocking) in diesel dual fuel systems is a very real concern which is very well explained in Dual Fuel Fumigation and all commercial systems address this issue to some degree. Due to the limited capability to control fuel mixtures to maximize fuel economy while minimizing detonation, budget diesel dual fuel systems have a limited ability to reduce fuel costs. Generally, the more expensive the system, the more sophisticated the operation so that there is a greater potential for reducing fuel costs and risk to your engine. The cost of the system becomes less important with the increase in fuel savings and reduction in risk. However, there are a lot of commercial, low-priced diesel dual fuel systems already installed on vehicles and their owners seem quite pleased with them. This article is an attempt to explain the operation of each system to help buyers make an informed decision.

Whatever system you decide to use, be sure to have the installation inspected and approved by a licensed LPG or CNG inspector in your jurisdiction BEFORE you put any fuel in it. Better yet, work with a local conversion shop on your project so that it meets both the spirit and letter of the regulations.

NEVER use a 20 lb cylinder as your propane motor fuel tank and NEVER run fuel lines inside the passenger compartment of your vehicle.