Bi-Fuel Vs. Dual Fuel: What’s the Difference?

With all the types of fuels out there that generators can run on, some of the terms can be confusing. From commercial and industrial generators to residential power options, I’m sure you’ve heard of natural gas, LPG propane (liquid, vapor), and of course diesel fuel, but what is the difference between bi-fuel and dual-fuel operations?

A bi-fuel generator runs on a system where the engine can use two types of fuel, but the fuels are kept separate during operation. Yes, the engine can switch between the two fuel options so that it is always using the type of fuel that is most efficient for the given circumstances. Some of these engines are controlled by a governor automatically, which then switches between the two types of fuel when a specific fuel is the most efficient choice.

In other circumstances, these engines allow the operator to determine the best fuel and switch between the two fuels. These engines can use either fuel exclusively in the absence of the other fuel source but will operate less efficiently when the operator chooses the least efficient fuel.

Numerous bi-fuel generators use LP vapor (propane vapor) and natural gas as the two fuel sources. Others switch between operating on natural gas (compressed or liquid) and gasoline, or natural gas and diesel. Certain fuels are best for some applications– like bi-fuel cars that may be designed to run on regular gas and natural gas, while a bi-fuel engine used in industry uses diesel and LP. 

Dual Fuel

A dual-fuel engine on the other hand can use two types of fuel at the same time in a mixture. Key phrase “MIXTURE.” This unit usually cranks up on one type of fuel, and a governor built into the system gradually adds the secondary fuel source until the optimal mixture of the two fuels is achieved for the most efficient operation.

Like bi-fuel systems, dual-fuel engines are usually capable of operating on just one of the fuel sources in the absence of the other. But, in numerous dual-fuel engines, a specific fuel is required for starting the engine.

For example, a dual-fuel generator starts by using diesel fuel and gradually adding a mixture of natural gas. The diesel ignites around 500-700 degrees F. The natural gas will not ignite until the temperature reaches 1,150-1,200 degrees F. Once the engine starts it can run on natural gas only or diesel only. But natural gas can’t be used to start the engine because of the lower temperature at start up when it is cold.

Bi-Fuel Engine Benefits

For starters, the bi-fuel engines run more efficiently. The big advantage of a bi-fuel system is that the efficient fuel for the task is always being used, so these systems are significantly more efficient to run when compared to a single-fuel engine such as a gas-powered car. Fuel storage is also streamlined, allowing more time between diesel fill-ups, or reducing the size of necessary storage tanks. 
Limiting the burning of diesel fuel, as a bi-fuel generator or other engines do, can dramatically lower emissions released into the atmosphere so sustainability comes into play. They can also aid in flare gas recapture, making use of by-products that would normally be wasted.
Of course, more efficient means saving money too. The difference in fuel costs can be upwards of 45% when you match bi-fuel up with a single-fuel system. With more efficiency you will also get more running time. 

Dual Fuel Engine Benefits

You will save money with a dual-fuel system as well. Thought they cost significantly more than traditional engines to buy, usually carrying a price tag 15-30% higher, but since the engine can run on a single fuel or a mix of fuels, it is less costly to run in the long run as it allows you to select whichever fuel is cheapest.
Reliability, flexibility, and fuel storage are also benefits of the dual fuel system. Since they can run on natural or LP gases, there is no need for a large diesel fuel tank so room for big tanks isn’t needed. If the gas flow is temporarily cut, the unit can run on diesel. The flexibility of a dual-fuel engine can also allow users to make use of alternative fuels such as sewage gas yet pair it with a more traditional fuel. Finally, dual fuel engines are also more sustainable.  

So bottom line—both dual and bi-fuel systems use two different kinds of fuels, but the bi-fuel system uses just one at a time whereas a dual fuel option can operate on a mixture. See one example of a dual fuel industrial generator at 88258. It’s an open skid Generac 600 kW that features a Doosan engine with 372 hours.