Diesel and Natural Gas Dual Fuel Nicholas Kenny, P.E. – Extension Irrigation Specialist, Texas A&M University
The direct-injection and What is Dual Fuel? injection of more fuel and compression combustion thus more power. In the traits of the diesel process Dual fueling is a cases of energy fuels, have consistently offered process that injects a more combustible material superior thermal efficiency secondary, gaseous fuel actually is forced into the compared to spark-ignition into the air charge of combustion chamber and systems (Otto cycle). In an internal combustion if sufficient oxygen can be addition to high efficiency, engine to optimize engine supplied (usually through diesel fuel carries more performance. Think of it the use of a turbocharger), energy value per gallon like nitrous oxide injection more power can be made. than other available liquid in a gasoline engine for In a similar fashion, this fuels and historically has racing or the more recent process can be optimized sold at a discounted price, trend of adding propane or for a reduction in consumed basically as a byproduct. methane in diesel trucks. In diesel fuel, basically These compounded benefits the case of nitrous oxide, replacing a portion of the have led to the broad oxygen concentration is energy needed from the application of the diesel increased in the air fuel primary fuel to accomplish engine across many solid- mixture, allowing for the the same amount of work. set industrial applications – especially at irrigation pumping plants. In recent years, personal and private demand for diesel fuel has increased and diesel fuel prices have steadily risen to that of a premium fuel. This evolution has had a dramatic effect on irrigation pumping costs, to the point where many farms cannot economically continue to pump irrigation water using diesel fuel. One technique that has proven very effective in reducing pumping costs at diesel pumping plants is injecting Air cooled Deutz engine on dual fuel. This picture was taken natural gas into the intake during an evaluation using a torque cell, natural gas meter air stream, or dual fueling. and diesel flow meter to ideally set fueling mixtures.
1 LSU AgCenter Pub. 3241-G: Diesel and Natural Gas Dual Fuel Table of common pumping plant fuels listed from lowest to highest with regard to cost per acre-inch of pumped water. Pumping parameters are 700 GPM, 400’ lift, 20 psi, and 65 percent pump and well efficiency, requiring a 128 horsepower engine load. 50/50 dual fuel.
BTU / Unit Cost / Unit Engine Fuel HP Cost / Efficiency Acre-In.
Natural Gas (MCF) 1,000,000 $ 4.50 23% 555 $ 4.11
Electricity (KWh) 3,413 $ 0.10 90% 135 $ 6.50
Dual Fuel (Diesel and NG) 29% 460 $ 9.24
Diesel (gal) 139,000 $ 3.50 35% 347 $ 14.36
Gasoline (gal) 124,000 $ 3.45 23% 555 $ 25.42
Propane (gal) 91,600 $ 2.80 23% 555 $ 27.93
Why Dual Fuel? gas into a port between the gas is turned off and then turbocharger and intake the engine is throttled Diesel fuel currently is manifold. A control valve down and turned off like a considered the third best (ideally a needle valve) normal diesel engine. Many option for powering an is installed in this line to operators have found it is irrigation pumping plant, control the natural gas very helpful to use a control preceded by electricity and volume. More complex valve that can be locked natural gas on a cost and systems (recommended) into one position as a flow operational basis. Diesel include automatic shut-off orifice to regulate the is the preferred liquid solenoids and a dedicated actual natural gas injection fuel in locations where fuel regulator to allow for flow. A second valve is continuously delivered more precise fuel control installed upstream of the electricity or natural gas is and natural gas shut-off in control valve to turn the not available. Although it the case of unanticipated natural gas flow on or off as may be a more beneficial engine shutdown. needed. decision to convert completely to natural gas To operate the process, It is not recommended or electricity, locations with the diesel engine is to exceed 50 percent existing diesel engines, a started on 100 percent natural gas mixture nearby natural gas pipeline diesel and throttled up (based on Btu content), and a large horsepower to operating speed under although field experience requirement will see great load. Then it’s throttled has shown many engines economic benefits by back to a predetermined can operate safely with fitting a diesel engine to be engine speed less than the a 60 percent natural gas supplemented with natural desired operating speed. charge. If excess natural gas fuel. The natural gas is then gas is injected, damage injected into the air intake may occur to the engine, How to Dual Fuel? to bring the engine up most notably witnessed by The first step in an to the desired operating audible knock, blow-by and operational dual fuel speed. Determining the decreased compression. system is the connection of operating points typically Further, engines that have the natural gas fuel supply requires trial and error been tested while operating to the diesel engine’s since pumping conditions on more than 60 percent intake tract. The simplest generally are unique to natural gas typically show method is to directly plumb each location. To shut the a dramatic reduction in pressure regulated natural engine down, the natural thermal efficiency. The
2 LSU AgCenter Pub. 3241-G: Diesel and Natural Gas Dual Fuel At this dual fuel pumping plant, natural gas is injected along the intake line just prior to the turbocharger and regulated by a gate valve. (Notice the yellow valve handle in the middle of the photo marked with a white circle.)
simplest method for setting and operation. Although Engine ratings are given the natural gas injection is natural gas can be injected for continuous operating to incrementally increase in these applications, the conditions and premature the natural gas injection diesel fuel flow is very wear and/or engine failure volume until an audible difficult to reduce. Older are likely to ensue if the change in engine sound engines with reduced injection of natural gas occurs and then to slightly compression and existing allows the engine to be reduce the amount of blow-by also have shown loaded beyond its rating. natural gas injected. The to be poor candidates for It also is very important safest method is to meter dual fuel applications due to operate the engine both the diesel fuel and to the increased stress from in a manner that keeps natural gas consumption to the additional combustion engine and exhaust gas determine what throttle and charge. Computer- temperature low while natural gas valve settings controlled engines typically dual fueling, since a large correspond to certain perform very well in a amount of raw natural operating conditions. dual fuel setting and gas is being expelled occasionally are fitted with with the engine’s exhaust Other Information a diesel flow meter that can (the natural gas fuel be very helpful in setting injected in the intake also Not all engines are good fuel ratios. is scavenging during the candidates for dual fuel exhaust stroke). Exhaust applications. Repurposed It is not recommended combustion is much more diesel generator motors to use natural gas injection likely to be catastrophic have proven difficult to to increase engine power with dual fuel. dual fuel because of the in a solid-set situation. mechanical governor design
3 LSU AgCenter Pub. 3241-G: Diesel and Natural Gas Dual Fuel www.LSUAgCenter.com
Louisiana State University Agricultural Center William B. Richardson, Chancellor Louisiana Agricultural Experiment Station John S. Russin, Vice Chancellor and Director Louisiana Cooperative Extension Service Paul D. Coreil, Vice Chancellor and Director
Pub. 3241 G (200) 10/12
The LSU AgCenter is a statewide campus of the LSU System and provides equal opportunities in programs and employment.
4 LSU AgCenter Pub. 3241-G: Diesel and Natural Gas Dual Fuel