Bi-Fuel™ - Diesel and Natural Gas Generators

When specifying generators, one of the first considerations is which fuel to use, whether its a diesel generator or a natural gas generator. Generac provides a solution that combines the advantages of both natural gas and diesel fuels. Bi-Fuel is the simultaneous combustion of natural gas and diesel fuel in a single engine.

The only true bi-fuel system, Generac’s Bi-Fuel generatorsare EPA certified from the factory, tested and installed – all other bi-fuel systems are aftermarket systems retrofitted in the field. Generac’s Bi-Fuel system components are specifically engineered to integrate together, with full warranty and service support included.

  • Reduced Fuel Storage – Because natural gas is the primary fuel, smaller diesel tanks are viable. Less fuel stored on site can lead to easier permitting and lower fuel maintenance costs. In addition, indoor fuel installations with capacity limits per NFPA or local codes may become feasible.
  • On-Site Fuel – For some applications, on-site fuel is required or strongly preferred. With bi-fuel, if there is ever a problem with the natural gas supply, the generator automatically switches to 100% on-site diesel fuel without affecting operation. This meets the on-site fuel requirements for emergency systems as referenced in NEC700 and NFPA110.
  • Lower Cost – The cost of a midrange natural gas generator is approximately twice that of a comparable diesel unit. Bi-fuel offers many of the benefits of natural gas for only slightly more than a diesel-powered system and has a higher thermal efficiency than natural gas solutions. This may translate into operational fuel savings based on traditional fuel costs.
  • Reduced Exhaust Emissions – Bi-fuel generators emit about 30% less nitrogen oxides and 50% less particulate matter than comparable diesel-only units for an environmentally friendly solution.

What does Bi-Fuel™ refer to on standby generators?

Bi-Fuel is the simultaneous use of two different fuels to power the engine on a standby generator set. For Bi-Fuel operation, Generac uses a mixture of diesel fuel and natural gas (NG) in a diesel engine.

Is this different than dual-fuel?

Unfortunately, there is no clear answer. Both bi-fuel and dual-fuel are used within the industry to describe the concept of simultaneous combustion. In addition, both terms have also been applied to redundant fuel supplies where a secondary fuel is used only after the primary fuel is depleted or intentionally switched off. Therefore, it is important to understand how the terms are being used when comparing products. Generac uses the term Bi-Fuel for the simultaneous combustion of both fuels, and dual-fuel to describe a system in which liquid propane vapor serves as a backup fuel source in a natural gas system. This system is available as an option on a number of our gaseous fueled generators.

Is the Bi-Fuel concept a new technology?

No. Bi-Fuel has been around since the early 1900’s. However, early designs lacked adequate controls to make it very effective. Since that time, much development has occurred and control technology has advanced to make Bi-Fuel operation efficient and economical. Generac has developed a microprocessor-based control system that meets the challenge of maintaining an optimal balance of diesel and NG across the power range of the engine.

How does the Generac Bi-Fuel system work?

Generac uses relatively low cost, high volume diesel truck engines that have been well proven in demanding trucking applications. The engine starts on 100% diesel fuel. As soon as the coolant reaches a minimum temperature and the generator starts to accept load, natural gas is metered into the combustion air stream just before the turbocharger. As compression occurs, the diesel fuel ignites normally and provides the spark required to ignite the natural gas.

As load is applied, the amount of natural gas is increased and the amount of diesel fuel is decreased. We have conducted comprehensive testing and fuel ratio mapping to ensure safe, reliable operation under all combinations of load and temperature. Our PowerManager® control system continually monitors factors such as coolant temperature, intake manifold temperature and pressure, kW load and engine speed. The fuel mixture is instantly adjusted as needed. Under typical conditions, the operating fuel mixture will consist of at least 70% natural gas.

What are the benefits of Bi-Fuel?

  • Dramatically extended run times with available on-site supply of diesel fuel
  • Lower capital cost per kilowatt (kW) than spark-ignited engines
  • Improved reliability with redundant fuel supply
  • Reduced diesel fuel storage
  • Reduced fuel maintenance
  • Lower exhaust emissions than diesel engines

Is Bi-Fuel operation detrimental to the diesel engine?

No. In fact, the cleaner burning characteristics of NG result in less contamination of lubricating oil and reduced engine wear. In addition, peak cylinder pressures and exhaust temperatures, the key factors in engine wear, are lower during Bi-Fuel combustion than during diesel-only operation.

The PowerManager controller protects the engine by sensing the signature vibration signal created as conditions approach pre-ignition and immediately reduces the supply of natural gas before pre-ignition can occur. If the condition persists, natural gas is shut off, operation continues on 100% diesel fuel and an alert is issued. Extensive testing has shown that a Generac Bi-Fuel engine will have a longer operating life with extended service intervals and reduced maintenance costs than a standard diesel engine.

What happens if natural gas pressure drops or the supply is cut off?

The system will automatically and seamlessly switch to 100% diesel operation with no loss of power during the transition. It’s important to remember however, that the system cannot run on 100% natural gas because the ignition of the diesel fuel provides the spark that ignites the natural gas.

Can I monitor the amount of natural gas being used by the engine?

Yes. Our GenLink® software allows you to monitor all aspects of generator performance, either locally or remotely. GenLink can display natural gas flow both numerically and graphically.

How does the transient response of the Bi-Fuel engine compare to a standard diesel engine?

The Bi-Fuel engine’s transient load response is the same as a diesel engine. The standard diesel governing system is always active. During sudden load changes, diesel instantly becomes the dominant fuel so the engine will react just like a normal diesel engine. As a result, the Generac Bi-Fuel maintains the superior transient response of a diesel engine while providing the benefits of natural gas operation.

Can Generac Bi-Fuel generators be used in prime power applications?

No. At this time Generac Bi-Fuel generators are rated for standby applications only.

Are Generac’s Bi-Fuel generators UL Listed?

Yes. As with all Generac generators, our Bi-Fuel units are UL 2200 Listed for Stationary Engine Generator Assemblies. Both UL Listing and CSA Certification are available options on these units.

Where is my generator made?

Generac generators are made in the United States. Manufactured by Generac Power Systems, Inc. in one of three manufacturing facilities in Wisconsin.

Single Unit Bi-Fuel
Power Rating Model Engine
500kW SB500 15.2L
600kW SB600 18.1L
MPS Bi-Fuel
Power Rating Model Engine
500kW MB500 15.2L
600kW MB600 18.1L

Standby Bi-Fuel Genset Models

Warranty Type

Warranty Coverage
Standard (single genset) 2 Year Basic
Standard (MPS) 2 Year Comprehensive
Optional 5 Year Basic
Optional 5 Year Extended

Note: Optional 2-Year Extended, 5-Year Basic and 5-Year Extended warranties are only available for units installed in the United States or Canada.

Modular Power System Bi-Fuel Genset Models

Warranty Type

Warranty Coverage
Standard 2 Year
Optional 1 Year Extended
Optional 5 Year Basic
Optional 5 Year Extended

Note: Optional 2-Year Extended, 5-Year Basic and 5-Year Extended warranties are only available for units installed in the United States or Canada.

See your industrial dealer for warranty details.

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