Overview

A Bi-Fuel or Dual-Fuel (either term is correct) engine system utilizes both natural gas and diesel fuel to operate.  After conversion to bi-fuel an engine is capable of running on either 100% diesel fuel or a diesel fuel and natural gas mixture, consisting of up to 90% natural gas. The natural gas can be either compressed natural gas (CNG) or liquid natural gas (LNG). However, the engine is never capable of running on natural gas alone.

There are two possible bi-fuel conversions—high speed conversion and low speed conversion. For low speed conversions, gas is injected into the manifold by separate hardware and controlling software. For engines running at higher speeds, the gas is mixed with air before the turbocharger. Low speed conversion allows substitution of 70-90% natural gas for diesel, and high speed conversion allows substitution of 50-80% natural gas for diesel.

The Bi-Fuel conversion does not require any modifications to the diesel engine. All of the conversion hardware is mounted externally to the engine, and does not void most engine warranties. The conversion generally does not cause any horsepower loss as compression ratios are not altered. 

The Bi-Fuel conversion technology does not alter an engine’s efficiency. For each gallon of diesel fuel displaced, 140 cubic feet of natural gas will be consumed. Therefore, for each gallon of diesel fuel displaced, an equivalent gallon of natural gas will be consumed.

Appling the bi-fuel conversion technology will result in a cost savings that is dependant on the relative costs of the fuels.  If diesel fuel and natural gas have similar costs on a per-heating value basis, savings will be minimal. However, if natural gas costs are much cheaper than diesel fuel, the conversion will result in substantial fuel savings.

In addition to fuel and operating cost savings, converting an engine to bi-fuel will have a positive environmental impact.  As natural gas is a cleaner fuel than diesel, combusting an increased percentage of natural gas will decrease emissions.  This will allow an existing engine to meet more stringent environmental regulations.

Application

The bi-fuel conversion works best for large stationary engines. Advantages of bi-fuel generators include smaller diesel facilities and longer runtimes during extended power outages for generators. As engines of this size are generally used for standby generators, the technology is best used for customers who need an uninterrupted power supply such as:

• Hospitals
• Apartment complexes
• Hotels
• Manufacturing facilities

Additionally, bi-fuel conversion has been applied to peak power shaving facilities at electrical power utilities.
 
Manufacturers

Clean Air Power
www.cleanairpower.com

ComAp LLC
www.comapllc.com/bi-fuel-conversion.php

Energy Conversions Inc.
www.energyconversions.com

Generac
www.generac.com

GTI Altronic, Inc
www.gti-altronicinc.com

Innovative Technology Group Corp.
www.innotechgroup.com

Westport Innovations Inc.
www.westport.com

Additional Resources

http://en.wikipedia.org/wiki/Bi-fuel_conversion
http://www.energetech.com/bi-fuel-faqs.htm