Natural gas is a combustible, gaseous mixture of simple hydrocarbon compounds, usually found in deep underground reservoirs. Pipeline quality natural gas is composed almost entirely of methane, but does contain small amounts of other gases, including ethane, propane, butane and pentane. A methane molecule is composed of one carbon atom and four hydrogen atoms (CH4).

The Bi-Fuel System has been designed for optimum performance using pipeline quality natural gas. Pipeline gas typically has little variation in gas quality and composition on a day to day basis and is normally made up of 80%-90% methane. The methane number of the fuel is important for Bi-Fuel operation as the combustion characteristics of methane differs substantially from ethane, butane, pentane, (collectively referred to as heavy-hydrocarbons) etc. Methane has a high auto-ignition temperature (approximately 1200° F) and a high amount of resistance to detonation, thereby allowing its use in high compression diesel engines. As the methane number of the fuel decreases, and the heavy-hydrocarbon number increases, the combustion characteristics of the fuel will change and may require a lower substitution percentage of natural gas.

For installation in colder climates, it is important to determine the gas composition during the winter months when gas companies may utilize propane "peak-shaving" to boost the Btu level of the fuel to meet high demand. Prior to installation of the system, a comparison of summer and winter gas analyses should be made to determine what allowance should be made, if any, in the calibration and/or operation of the system due to expected changes in the gas methane number. In recent years, liquid natural gas (LNG) peak-shaving has become the preferred method of meeting winter demand for many gas utility companies and this type of enrichment process maintains a more stable methane number throughout the year.

Other methane based gases can be utilized with the Bi-Fuel System such as wellhead gas and bio-gas. When utilizing gases other than pipeline quality, the following factors must be considered:

o Methane content
o Heavy hydrocarbon content
o Heating value
o Inert gases
o Moisture content
o Caustics
o Particulates

For reasons explained above, it is important to determine the methane and heavy-hydrocarbon content of the fuel, and possible ranges thereof, prior to installation of the Bi-Fuel System. If the fuel has heavy-hydrocarbons in excess of 20% in the normal gas stream, or alternately, can have periodic "slugs" of heavy-hydrocarbons, it may be necessary to decreases the gas substitution percentage and/or de-rate the engine during Bi-Fuel operation. The installer should be wary of so called "hot gas" which due to heavy concentrations of heavy hydrocarbons can have heat rates in excess 1200

What is good about Spark Ignited Engines

 There is no need for diesel fuel storage.
 The engines have only one fuel system to maintain.
 They are purpose built with optimized cam timing and a piston
compression ratio that best balances efficiency, emissions and power
with a specific fuel.
 Most (all non lean burn) can readily utilize catalytic converters on the
exhaust to accomplish quite good emission levels.
 OEM product support. (converting a small diesel engine to spark
ignited gas is generally not economically viable)

What is not so good about them

  It is common understanding that spark ignited engines don’t have the same power
density. It makes sense then that they will have a larger price tag for the equal
power (bigger engine for the same rating).
  Spark ignited engines have a different cam timing than diesels so generally they
will have higher exhaust gas temperatures. Combined high temperatures with the
dry gas fuel causes significantly higher valve seat wear rates.
 Spark systems have come a long way in durability but they are far from maintenance free.
Many engines have fairly short plug life while there are plugs special built to last longer they
are expensive Spark plug life can range from 600 hours to 1500 maybe 2500, longer if
conditions are good and special plugs are used. (When visiting a ASME ICE conference
in New Orleans I listened to a speaker explain the most current advances to spark
plug life.I asked him what the best most durable igniter system was?,
he smiled and said, “a diesel injector”.)
  Spark ignited engines have limits to fuel content, temperatures and power capacity.
Combustion knock is an operational limiting factor that ruins spark plugs.
Timing adjustment can help.

What is good about Dual Fuel Engines

Well first I will say that not all dual fuel systems are created equal. There were systems with different attributes but in general the following will be true.
 Keep your diesel engine, convert it and run with gas
 Fuel flexibility, if gas is interrupted full diesel operation is available
instantly while generating power.
 Full original power capacity in one form or another,it is system dependent.
 Diesel cam timing keeps exhaust cooler and provides better scavenging,
contributes to higher power density and longer valve life.
 Higher compression ratio, better efficiency, nearly all dual fuel engines have
better efficiency than spark gas.
 Diesel ignition, this is a huge one. You will have very long service intervals with
the ignition system (same as normal diesel injector service). Lean burn
combustion capacity, far beyond any spark ignition system, contributes to reduced
misfire, better efficiency, higher power density, reduced Nox emissions. Diesel
pilot fuel provides lubrication to valves and rings, when combined with clean gas,
3 maintenance service intervals are longer than straight diesel not shorter like spark
gas.
 Exhaust emissions, specifically Nitrogen oxides, CO2 and particulates are significantly reduced.
 Fail safe operation, if a problem exists with the gas system full diesel backup is
instantly provided.
 No changes should be made to your standard engine warranty (affected by the
attitude of local dealer)
 Should be noted that certain aspects of a lean burn spark gas and dual fuel are
similar.

What is not good about Dual Fuel

Here again we find differences with different systems.
• Dual fuel engines require diesel for ignition. Run out of diesel and you are not
running.
• Higher emissions of CO compared to straight diesel. Similar emissions of CO as
spark gas (with out catalytic converter).
• Two fuel systems to maintain. Keep in mind however that diesel fuel ignition is
less maintenance than spark systems and that the gas control system is mostly
maintenance free.Requires the support of additional supplier, not just the OEM.
• Engine warranty, if you still have a warranty on your engine, we have seen the
attitude of local dealers and distributors who immediately assume that this will
void your warranty. This is simply not the case and in the United States there is a
law that requires OEM’s to maintain their warranty in the presence of aftermarket
accessories (stated below). So what is not so good? Just overcoming people with
wrong understanding!
• Less oil contaminates leads to longer lasting engine, possibly by a factor of two.
Why is this not good? Well this is sort of a little joke but if you are a engine
dealer not selling rebuild parts its not funny. You will not sell major engine parts
like you would for standard diesel engines.

Diesel and natural gas fueled generators have been common solutions for industrial standby power applications for decades. Each has its advantages and disadvantages. Natural gas generators, though common in the under 150 kW market, are limited in larger kW applications due to significantly higher capital costs. Even so, natural gas generators offer numerous advantages compared to diesel solutions. The most noticeable is the extended run time offered by an endless supply of natural gas. This is a huge advantage given that refueling conventional diesel generators can be quite challenging during long-term outages. Hurricanes and storms can close roads, and area-wide outages can totally cripple refueling infrastructures.

Diesel generators are the market norm above 150 kW, but system designers must plan for the limitations associated with utilizing on-site diesel fuel. Storing small amounts creates the risk of running out of fuel. Storing large quantities requires on-going maintenance to prevent Contamination and degradation. In addition, fuel delivery from a main storage tank may require a system of pumps, solenoids, and isolation valves that can negatively impact the reliability of the generator during an outage.

Bi-fuel gensets offer the best of both worlds. At a cost that is only slightly higher than a diesel-only design, bi-fuel ensures the extended run time benefits of natural gas, plus a more manageable amount of on-site fuel.

THE BI-FUEL SYSTEM The Bi-Fuel System operates by blending diesel fuel and natural gas in the combustion chamber. This is achieved using a pilot-ignition, 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. Because of the high auto-ignition temperature of natural gas, the air-gas mixture will not ignite during the compression stroke, as there is not enough heat present to facilitate combustion.

Because the OEM air-intake and diesel injection systems are utilized by the Bi-Fuel System, no engine modifications are required for installation. The various components of the Bi-fuel System are installed externally of the engine, and at no time is the engine disassembled during installation. All OEM engine specifications for injection timing, valve timing, compression ratio, etc., remain unchanged after installation of the Bi-Fuel System.

The Bi-Fuel System requires a low pressure natural gas supply (approximately 2-5 psi) with a flow rate of approximately 8 scfh/kW (i.e. 500 kW=5,000 scfh).

The primary components of the Bi-Fuel System include:

• Bi-Fuel Control Panel
• Diesel Fuel Control Valve
• Gas Control Valve
• Manual Gas Valve
• Gas Solenoid Valve
• Air-Gas Mixer
• Gas Pressure Regulator
• Natural Gas Pressure Transducer Manifold Air Pressure Transducer Engine Vacuum Transducer(s) EGT Thermocouples

SAVINGS

Savings derived from the use of the Bi-Fuel System are the result of the differential between the cost per kWh charged by the utility and the cost per kWh to produce power with a Bi-Fuel generator. Due to the premium prices which utility companies usually charge for on-peak electricity, it is often most viable to operate the Bi-Fuel generator as a peak-shaver, whereby power is produced on-site only during those hours when electricity is at it's highest price from the utility.

In order to determine the cost of producing power with a Bi-Fuel generator, several factors must be considered including:

• Cost of natural gas
• Cost of diesel fuel
• Cost of maintenance program for generator
• Cost of future engine overhauls

Bi-Fuel Operations
Diesel use per hour: 10.5 gallons (35 gph x .30)
Diesel cost per hour: $9.98 (10.5 gph x $.095)
Gas use per hour: 34.3 therms*
Gas cost per hour: 34.3 therms x $0.40= $13.72
Total fuel cost per hour: $23.70
Total fuel cost per kWh: $0.047 ($23.70 ) 500kW)
Estimated maintenance: $0.020 (includes overhaul costs)
Total Bi-Fuel cost per kWh: $0.067

Savings
Bi-Fuel savings per kWh: $0.053
Bi-Fuel savings per hour: $26.50
Bi-Fuel savings per 1500 hours: $39,750 (750,000 kWh)
* 1 gallon #2 diesel = 140 scf natural gas based on #2 diesel hhv of 140,000 btu/gallon and natural gas hhv of 1,000 btu/scf; 35 gph diesel x .70= 24.5 x 140 scf = 3,430 scf = 34.3 therms

* 1 gallon #2 diesel = 140 scf natural gas based on #2 diesel hhv of 140,000 btu/gallon and natural gas hhv of 1,000 btu/scf; 35 gph diesel x .70= 24.5 x 140 scf = 3,430 scf = 34.3 therms

Benefits summary
Extended Run Times

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, indoors fuel installations with capacity limits per NFPA or local codes may become feasible.

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. Bi-fuel also has a higher thermal efficiency than natural gas solutions. This may translate into operational fuel savings based on traditional fuel costs.

On-Site Fuel
For some applications, on-site fuel is required or strongly preferred. With the bi-fuel solution 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.

Reduced Exhaust Emissions
Bi-fuel generators emit about 30% less nitrogen oxides and 50% less particulate matter than comparable diesel-only units. This is consistent with the market’s preference for environmentally friendly solutions.

BI-FUEL "FAQ'S"

What does "Bi-Fuel" mean?
In simple terms, Bi-Fuel can be defined as the simultaneous combustion of two fuels. In the case of the 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.
What about "Dual Fuel"?
The terms Bi-Fuel and Dual Fuel are often used interchangeably, however, the U.S. EPA defines Dual-Fuel as "...engines or engines that have two separate fuel systems and are designed to run on either an alternative fuel or conventional gasoline, but using only one fuel at a time." (A Guide to the Emissions Certification Procedures for Alternative Fuel Aftermarket Conversions, January 1998)
Will my engine have to be modified to operate on the Bi-Fuel?
No. The 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 conversion hardware is mounted externally on the engine and does not require modification of the engine or alteration of any critical engine parameter.
What about my engine warranty?
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. In practice, if a converted engine has a failure under warranty, the OEM, in conjunction with technical personnel, make a determination as to the cause of the failure. If the cause is obviously unrelated to Bi-Fuel, the OEM's have historically honored the warranty and repaired the engine. If the cause is determined to be Bi-Fuel related, the manufacturer of the Bi-Fuel System will cover repair costs under it's warranty program.
Why can't the engine use 100% natural gas?
Because of the very high ignition temperature of natural gas (approximately 1300°F), 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.
Will my engine lose power after conversion to Bi-Fuel?
Under normal circumstances, engines converted to the 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- In some circumstances, the engine may be de-rated in Bi-Fuel mode due to shortcomings in gas supply composition and/or quality.
Will my engine run hotter on Bi-Fuel?
The 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 a/r-fuel ratios during Bi-Fuel operation remain largely equivalent to 100% diesel operation, resulting in normal peak exhaust gas temperatures and associated peak engine thermal loads.
What about efficiency?
As explained above, the 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 approximately 140 cubic feet of pipeline quality natural gas (based on 129,000 btu/gallon # 2 diesel & 930 btu/scf natural 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. Note: 1 m3 of natural gas = 1 liter # 2 diesel.
What effect will the System have on the durability of my engine?
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 Bi-Fuel 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.
What are the economic benefits to operating on Bi-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) may also contribute

Conclusion

The introduction of bi-fuel technology represents a tremendous advancement in the standby power industry. System designers have continually struggled with issues of fuel system reliability — too much fuel and it goes bad; too little fuel and it runs out. With tremendous increases in run time and the minimal use of diesel fuel, bi-fuel generators address these major fuel reliability issues and offer environmental advantages