Bi-Fuel vs. Dual-Fuel Engines

Confusion exists regarding the terms bi-fuel and dual-fuel engines. There is further confusion related to vehicle engines and constant speed engines used in industrial applications. Lastly, small consumer and residential applications such as emergency power generators add another layer of “mixed” understanding. Please read on for clarity on the two terms.

Two different fuels are used in a bi-fuel system, but they are not combined while it is operating. The engine can switch between the two, ensuring that it always runs on the fuel that is most effective or available in a given situation. A control system which automatically alternates between the two fuel types when one is the more efficient option is used in some of these engines.

With other bi-fuel engines, the user can freely alternate between the two fuels. In the event that the optimal fuel source is unavailable, these engines can run solely on the other fuel type; however, they will perform less efficiently.

Certain bi-fuel generators employ natural gas and propane as the two fuel sources. Others switch between operating on natural gas (compressed or liquid) and gasoline or diesel. Most constant speed bi-fuel engine applications in industry uses diesel and LP.

A dual-fuel system can run on two different kinds of fuel in combination at the same time. Typically, it starts off using one fuel type and then gradually adds the second fuel source through a separate system until the ideal blend of the two fuels is reached for effective operation.

Similar to the bi-fuel system, a dual-fuel engine can typically run on only one fuel source when the other isn’t available. On the other hand, a certain fuel is needed to start the engine in many dual-fuel engines.

For instance, a dual-fuel generator progressively adds a blend of natural gas after initially starting up on diesel fuel alone. Diesel fuel can ignite at relatively low temperatures of 500 to 700 degrees Fahrenheit, but natural gas won’t ignite until temperatures reach 1,150-1,200 degrees Fahrenheit. Thus, natural gas cannot be used to start the cold engine. Diesel fuel is used to start the engine and allow it to warm up to temperatures at which natural gas will ignite. Once the engine warms up, it can run on natural gas alone, diesel fuel alone, or a combination of the two.

OptiBlend® technology is a Dual-Fuel system primarily suited for retrofit of 200-2000 kW diesel power generators. OptiBlend® optimizes existing assets to extend runtime through diesel displacement, lower operational cost with cheaper fuels, and reduce CO2, NOX, and other emissions inherent in diesel engines.