Cummins Dual Fuel Engines

In the oil and gas market, the fuel bill is one of the largest contributors to the total cost of operation. The rapid expansion and abundance of natural gas in some areas of the world is driving a dramatic cost advantage of natural gas over diesel fuel, making natural gas a very economical fuel source for oil and gas operations. For operators of high-horsepower oil and gas equipment, where power density is critical and large quantities of fuel are burned, Cummins Dual Fuel provides an opportunity for impressive reductions in total fuel costs by using a technology that substitutes natural gas for diesel fuel in the engine combustion process.

What is Dual Fuel and How Does It Work?
A dual fuel engine is based on a traditional diesel engine, with the addition of dual fuel-specific hardware. When the engine is operating in dual fuel mode, natural gas is introduced into the intake system. The air-to-natural gas mixture from the intake is drawn into the cylinder, just as it would be in a spark-ignited engine, but with a leaner air-to-fuel ratio.

Near the end of the compression stroke, diesel fuel is injected, just as it would be in a traditional diesel engine. The diesel fuel ignites, and the diesel combustion causes the natural gas to burn. A dual fuel engine can operate either on 100 percent diesel fuel or the substitution mixture of diesel and natural gas, but it cannot operate on natural gas alone. Dual fuel engines deliver the same power density, torque curve and transient response as the base diesel engine does.
dual fuel overview
A critical parameter for dual fuel operation is the substitution rate, which is defined as the fraction of the total fuel energy that is provided by the natural gas. Substitution rates vary by load. A maximum substitution rates of 70 percent can be achieved with Cummins Dual Fuel for applications with high load factors.

The figure below illustrates a typical well servicing application substitution rate through the operating range. The sweet spot of operation is where the highest substitution rates are achieved, delivering the greatest reduction in fuel costs.
dual fuel rates
There is also flexibility with the quality of gas an operator uses. An operator can run on a lower-cost, lower-quality gas at a lower substitution rate, or use a higher-quality fuel at a slightly higher cost with a higher substitution rate.

In the United States, dual fuel engines must meet the applicable compression ignition emissions regulations. While specifics may vary, typically an oxidation catalyst to lower carbon monoxide (CO) and non-methane hydrocarbon (NMHC) emissions is required.

Cummins and Dual Fuel
Cummins will produce dual fuel engines for well servicing applications. The engines using Cummins Dual Fuel technology substitute diesel fuel with natural gas in the combustion process, reducing the amount of diesel fuel required to operate frac equipment. The first engine in the Cummins Dual Fuel portfolio for well servicing will be the QSK50, followed by dual fuel for land-based drilling applications, with other QSK Series engines to follow, including engines capable of meeting worldwide emissions regulations.

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