Introduction to Bi-Fuel Technology

The GTI Bi-Fuel System from Altronic offers an affordable and efficient means of operating industrial diesel engines utilizing both diesel and natural gas (or other available gas) as fuel sources. This innovative, patented system, which requires no modification to the internal components of the engine, allows for operation on natural gas up to a maximum of 70%* of the fuel required to maintain the desired speed and load. Reduced fuel costs and extended runtime are just a few of the benefits of Bi-Fuel operation.

The GTI Bi-Fuel System operates by blending both diesel fuel and natural gas in the combustion chamber. This is achieved using a fumigated gas-charge design, whereby natural gas is pre-mixed with engine intake-air and delivered to the combustion chamber via the air-intake valve. The air-gas mixture is ignited when the diesel injector sprays a reduced quantity of diesel fuel into the chamber.

This diesel “pilot” acts as the ignition source for the primary air-gas combustible mixture. Because the Bi-Fuel System utilizes the OEM air-intake and diesel injection systems, no internal engine modifications are required for installation.

Features

No engine
modifications required
No power or
efficiency losses
Low cost and easy
to install
Reduces operating
costs
Extends run-time of
standby engines
Lowers emissions
No high-pressure
gas supply
State-of-the-art
controls and monitoring

Major Bi-Fuel System
Components and Subsystems

Air-Fuel Mixer

The AGM-PV is a venturi carburetor that provides the optimal demand signal for use in supplying the required air/gas mixture to the engine. The proprietary design is manufactured to exacting tolerances from anodized aluminum for corrosion resistance and highly reliable service.

Gas mixes with the incoming air stream through a slot in the inner diameter of the mixer throat. The width of this slot is adjusted by means of a collar on the outside of the mixer body. This collar serves as the fixed power valve and is used to adjust the maximum allowed substitution rate of the system. Electronic pressure sensors, mounted to the mixer, sense the pressure in the mixer plenum.

Standard Gas Train

Conditioning and regulating the natural gas prior to admission into the engine is a critical part of the GTI Bi-Fuel system. The system “gas train” includes a 50-micron fuel filter, a manual shutoff valve, an electrically operated solenoid valve actuated in the event of an emergency or for system shutdown, and a zero-pressure, demand-type gas pressure regulator.

This latter component reduces the inlet gas pressure (.5–4 psig) to roughly atmospheric pressure. With a negative outlet pressure, the design allows the system to use a “demand” control scheme whereby engine intake airflow determines the gas flow of the engine. As engine load changes, corresponding changes in intake air volume automatically draw additional fuel into the mixer.

GTI+ Gas Train

The GTI+ system utilizes a fully electronic, advanced gas train design, which includes the Altronic AGV5 Fuel Valve, a microprocessor-based smart valve equipped with a fast-acting voice coil for rapid and accurate response. 

The AGV5 serves as both the zero governor pressure controller and fuel valve to control the bi-fuel substitution rate across the engine load range. The valve responds in closed-loop control to an electronic pressure signal within the mixer housing, ensuring that the fuel demand at the mixer is satisfied at any given time and eliminating pressure droop associated with pneumatic pressure control systems. This closed-loop control minimizes the effects of pressure drops between the outlet of the gas train and the mixer inlet. This allows the desired substitution rates to be met, while maintaining the fundamental safety characteristics of a zero pressure draw-through design. The AGV5 is a proven design that has been utilized as the fuel control device in hundreds of gas engine applications. Its soft-seat poppet is highly tolerant of gas stream contamination and offers fail safe reliable service. Since the AGV5 is rated to a higher pressure, the gas train can accept gas supply pressure of up to 50 psig, eliminating the need to reduce higher gas supply pressures to lower gas train inlet pressures with an added primary regulator. The new enhanced gas train also uses a highly-reliable, automatic, fast-acting, industrial shutoff valve to provide dual shutoff capability. The actuator is equipped with the ability to visually confirm the OPEN/CLOSED position of the valve.

Control Panels

The Control Panels are based on proven Altronic controllers and provide state-of-the-art engine control and safety shutdown monitoring. The system is designed specifically for GTI Bi-Fuel applications and is straight-forward and easy to operate.

The panel monitors a number of pressure and temperature points and returns the engine to 100% diesel operation should any parameter deviate from its normal range. In addition, an hourmeter function tracks the operating hours when in Bi-Fuel mode.

GTI Bi-Fuel® System Project Overview:

Zenergy

  • 60% savings on diesel costs

  • Environmentally friendly—lower emissions (NOx, SO, Opacity, NMHC) very important considering current and future environmental regulations.

  • No typical black smoke. • Zero downtime after 6000 hours

  • Bi-Fuel®  system runs smooth and clean—better than straight diesel.

Alternative Fuel Systems In North Dakota, the demand for electricity to operate new oil well drilling sites is overwhelming. The number of new wells averages 160 per month and in most cases the wait for electric service is 8 to 12 months. ECO/AFS has outfitted several rental generators with Bi-Fuel® systems. These generators are operating on 60% well gas and 40% diesel. Jim Fehlauer, Field Superintendent for Zenergy, had this to say about the GTI Bi-Fuel® system, “Thanks to Industrial Equipment Sales and Service and ECO/AFS for providing Zenergy with quality equipment and (Left to right) Jeff Anderson (ECO Alternative Fuels Systems) Jim Fehlauer (Zenergy) Sam Osborne (Arrow Pipeline LLC) quality service. This combination has allowed Zenergy to get our wells on line and producing while we wait for electricity. We had seven GTI Bi-Fuel® generators running 24/7 for 8 months with zero down time…which really helps our bottom line.”

Fehlauer concluded, “Though we have not needed it, we appreciate the f lexibility of using both fuels. If well gas is interrupted the engine switches to straight diesel without a hitch. This helps us to avoid costly down time.”

I highly recommend the GTI Bi-Fuel® system. Zenergy is currently running twelve units, and I will not use anything else.

Savings

The savings realized by running the GTI Bi-Fuel System is directly related to the cost of diesel fuel, cost of gas, and the number of hours of operation. The following is an example is a cost comparison between running a 1000 kW generator on 100% diesel and on Bi-Fuel with a 65% gas-to-diesel ratio in continuous operation. A number of assumptions are made in this example which are clearly stated in order to clarify the calculations.

FACTS AND ASSUMPTIONS
Fuel consumption @ 1000 kW: 54 gph (100% diesel)
Hours per year 8000
Gas/Diesel ratio 65%
Diesel cost ($/gal) $3.50 per gallon
Natural gas cost ($/mcf) $11.00 per mcf
hhv of #2 diesel 140,000 btu/gal
hhv of natural gas 1,000 btu/scf
Gas Equivalent Gallon (GEG) 140 scf/gal
100% DIESEL OPERATION
Diesel use per hour 54 gallons
Diesel cost per hour $189.00 (54 x $3.50)
Diesel cost per year $1,512,000 ($189 x 8000)
BI-FUEL OPERATION
Diesel use per hour 18.9 gph (54 x 0.35)
Diesel cost per hour $66.15 (18.9 x $3.50)
Gas use per hour 4914 scf (54 x 0.65 x 140)
Gas cost per hour $54.05 (4914/1000 x $11.00)
Total fuel cost per hour $120.20 ($66.15 + $54.05)
SAVINGS
Bi-Fuel Savings per Hour $68.80 ($189.00 -$120.20)
Bi-Fuel Savings per 8000 hours $550,368.00 ($68.90 x 8000)

Bi-Fuel System FAQs

In simple terms, bi-fuel can be defined as the simultaneous combustion of two fuels. In the case of the GTI Bi-Fuel System, natural gas is utilized in conjunction with diesel fuel to operate the engine. After conversion, the engine is able to operate on either 100% diesel fuel, or alternately, on a mixture of diesel fuel and natural gas (or other methane based fuels). At no time is the engine able to operate on natural gas exclusively.

No. The GTI conversion technology has been designed to allow for in-field retrofit of diesel engines without the need to change or modify the design of the engine. The GTI conversion hardware is mounted externally on the engine and does not require modification of the engine or alteration of any critical engine parameter.

Most OEM engine warranty programs do not prohibit the use of aftermarket parts or technologies. In brief, the policy of OEM’s is that they neither recommend nor endorse aftermarket technologies; however, the use of these products does not automatically void the validity of the engine warranty. If the cause is unrelated to bi-fuel, the OEM’s have historically honored the warranty and repaired the engine. Additionally, all GTI Bi-Fuel components that fail within the warranty period will be covered under the GTI Bi-Fuel warranty policy.

Because of the very high ignition temperature of natural gas (approximately 1300 degrees Fahrenheit), sufficient heat is not generated during the diesel compression stroke to ignite 100% natural gas. As such, dedicated gas engines employ spark plugs and an ignition system to facilitate combustion of the air-natural gas mixture. In contrast, during bi-fuel operation, a reduced quantity of diesel fuel acts as the ignition source for the air-gas mixture; this process is often referred to as pilot ignition.

Under normal circumstances, engines converted to GTI Bi-Fuel do not suffer any horsepower losses while operating in bi-fuel mode. Because the system maintains OEM compression ratio values and does not incorporate an air-throttling device, peak horsepower and efficiency levels of the converted engine remain on par with 100% diesel operation.

GTI Bi-Fuel technology has been designed to maintain OEM specifications for all engine temperatures including engine coolant temperature, oil temperature, exhaust gas temperature and intake air temperature. The Bi-Fuel System replaces diesel fuel normally consumed by the engine with an equivalent quantity of natural gas, relative to the heat value of each fuel. As such, engine air-fuel ratios during bi-fuel operation remain largely an “equivalent gallon” of natural gas is consumed resulting in similar engine fuel efficiencies.

The GTI Bi-Fuel System replaces diesel fuel with an equivalent quantity of natural gas. This process results in the same net fuel burn vs. load as would be experienced during 100% diesel operation. For each gallon of diesel fuel displaced during bi-fuel operation, there is a corresponding consumption of methane-based gas. Thus, for each gallon of diesel fuel displaced during bi-fuel operation, an “equivalent gallon” of natural gas is consumed resulting in similar engine fuel efficiencies.

Generally speaking, operation in bi-fuel mode has no negative effects on engine wear rates and durability. As explained above, because engine thermal loads are equivalent to 100% diesel operation, no excess wear of combustion chamber components (pistons, rings, valves, injectors, etc.) occurs. In addition, many users of the GTI Bi-Fuel System have reported positive benefits relative to engine wear including extended oil change intervals and extended time between overhauls. This is primarily the result of the cleaner burning characteristics of natural gas compared to diesel fuel.

Fuel cost savings resulting from operation in bi-fuel mode will vary according to the respective cost of each of the fuels. If there is a significant cost differential between the cost of diesel fuel (per gallon, liter, etc.) and the equivalent quantity of natural gas (heat value basis) in favor of the natural gas, significant fuel cost savings would result. The closer the fuels are in price, the lower the fuel cost savings will be during bi-fuel mode. In addition to fuel cost savings, engine maintenance savings (as explained above) and extended runtime (up to 3.4 times longer) also contribute to the economic benefit of bi-fuel operation.

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