Kit Converts Diesel Irrigation Engine to Natural Gas

While diesel prices have dropped compared with the astronomical charges a couple of years ago, irrigators are always looking for ways to trim this expense. So when Jerl Joseph saw a display for a kit that converts a diesel irrigation engine to natural gas, he decided it was worth a try.

Today, two of the diesels powering pumps and pivots on the operation he runs with his son, Eric, near Hampton, Nebraska, run primarily on natural gas.

"One of the engines is a four-cylinder Case IH engine that supplies a quarter-section pivot plus 40 acres across the road that are still furrow-irrigated," Joseph says. "The other is a four-cylinder John Deere engine on an 80-acre pivot. Fortunately, there were already natural gas lines running to both locations. They were put in back when the fields were flood-irrigated."

The original engines on those fields weren't large enough to handle a center pivot, though. So Joseph replaced them with diesel power plants. To go full circle back to natural gas, all the Josephs had to do was some plumbing on the gas pipes supplying the engine and some installation of conversion kits they acquired from C&E Clean Energy Solutions in Sturgis, South Dakota. The conversion components included the appropriate gas valves and solenoid, a fuel-injection manifold that fit between the air intake and the turbocharger, and a pyrometer (or temperature gauge) that was installed in the exhaust manifold to protect against overheating.

Conversion halved fuel costs
"Natural gas is still a lot cheaper than diesel, even with the price drop (with diesel). As a result, it cost about half as much to irrigate those two fields last year as it has in the past," Joseph says, noting that 2014 was the first year of operation for the John Deere conversion and the second season on the Case IH unit.

According to sources at C&E Clean Energy Solution, there are basically two ways to introduce natural gas into a diesel engine. One is to inject gas into the airstream at a single point via a fumigation nozzle, which is the route the C&E conversion takes.

The alternative is to introduce natural gas into the cylinder via an injector that is similar to a fuel injector.

Glow plug issues
Unfortunately, natural gas can't be introduced into the airstream while glow plugs are on or it could ignite, due to its higher combustibility. Consequently, any engine with glow plugs must be started on straight diesel fuel and brought up to operating temperature before the gas flow is started.

On the other hand, natural gas will not combust by itself in the engine. The heat of compression is not sufficient to ignite it. Hence, natural gas needs some diesel to act as a liquid spark plug and to start the ignition process.

"It doesn't take much diesel fuel to ignite the gas, though," Joseph says. "So diesel consumption is held to the bare minimum. Yet, it's still enough to keep the lift pump, injector pump, and injectors lubricated as normal."

Metered by vacuum
The amount of engine vacuum determines the amount of natural gas introduced into the engine in the airstream. Moreover, because natural gas combusts so much more quickly than diesel fuel, the result is a very complete ignition and a very clean burn. That, in turn, means less soot is generated and, thus, deposited into the crankcase, providing the potential for longer oil change intervals.

"The best part of the conversion is that you can go back to 100% diesel at any time," Joseph says, noting that kits are sized for engine horsepower and fuel consumption.

A kit costs from around $1,300 (for <75-hp. engines) up to $3,400 (for <750-hp. engines). "If diesel becomes less expensive than natural gas or the flow of natural gas is interrupted, I can easily go back to diesel," he says.