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Generator Fuel: Diesel, Natural Gas, or Both?


#Generator Fuel

Diesel generators have ruled the industrial-scale generator roost for almost as long as the diesel engine has been around. But as the market shifts, environmental concerns become more prevalent, and new technologies are developed, alternative fuel types are becoming viable options for many applications.

With 20 years of experience working in the automotive industry, a focus on injection systems and on diesel and dual-fuel engines, a PhD in fluid dynamics, and a stint at Westport, developing their HDPI technology for natural gas engines, Anne-Gael Favennec knows a thing or two about fuel systems.

We spoke with Favennec about the pros and cons of diesel versus natural gas commercial generators. We also got the scoop on dual-fuel systems.

The Title-Holder: Diesel

Diesel’s efficiency has long kept it at the top of the generator fuel pecking order. “You consume less fuel with diesel than you do with gasoline,” explains Favennec. “So that’s why, most of the time, all those big engines and generators run with diesel.” Aside from the obvious cost benefit, diesel’s efficiency keeps storage requirements low. This makes diesel a leading choice for remote operations, where fuel storage is a major concern.

While diesel storage is more straightforward than natural gas storage, it’s not perfect. If stored too long, diesel becomes contaminated and can damage generators, clogging filters or introducing excess water into the system.

Another downside to diesel, as anyone tasked with environmental compliance will attest, is emissions. Favennec echoes this sentiment: “One of the main problems with diesel is that you create particulates,” she says. ”And now, we are more and more interested in reducing those emissions on all those pollutants. So if you’re working with industrial generators, one of the main things you’ll want to do is to first reduce your consumption, and then reduce your pollutants.”

Diesel’s efficiency might help with consumption, but the reduction of pollutants is where natural gas comes in.

The Challenger: Natural Gas

“An advantage when you’re using natural gas is that you do not create any particulates,” explains Favennec. This can be an attractive characteristic to project managers who are trying to keep their emissions low.

Furthermore, with the cost of natural gas as low as it is, running natural gas generators could also make sense in terms of cost reduction. Favennec acknowledges, though, that “the cost is low, but you’ll need more gas to have roughly the same amount of energy as with diesel. So the problem will be the storage.”

Case Study:  reducing flare gas.

The storage problem is why natural gas is normally used in cases where there is a fuel source nearby. That source is typically a pipeline, or, as was the case for one of our clients, a gas plant.

For remote projects with no gas line or other source nearby though, storage poses a real problem. “In the tank, you will have less energy if it’s a gas than if it’s a liquid,” explains Favennec, “so maybe you’ll have to compress your gas to have liquid natural gas [to increase the amount of energy you can store]. But if you do so, then you need to use another technology to store it, like a cryotank. So it starts to be complex.”

Favennec believes that natural gas generators have wider urban applications not only because of the access to pipelines, but also because of its cleanliness. “You can imagine, you have a diesel generator, you have a big black fog, it smells and it’s awful,” she says. “If you’re in the middle of the city, maybe you’ll think ok, it may be more interesting to use natural gas because all the impact on the environment, and on the people around me, will be lower.”

The Cooperative Approach: Dual Fuel

For a basic concept—combining two fuels in one system—dual fuel can be frustratingly complicated. For starters, there is the terminology. There is dual fuel, and bi-fuel, and an apparent confusion between industries and the US Department of Energy over which is which.

The terms refer to two different ways of combining fuels: either by mixing them, at varying ratios, or by running them separately, depending on which fuel is more readily available.

Favennec has seen the term “dual fuel” refer to both of these types of system.

The advantages of a dual fuel system are obvious: in a system which can use one fuel type or the other, you have a built-in backup when one fuel type is unavailable.

A system that allows mixing of diesel and natural gas can harness the efficiency and higher torque of diesel, while also taking advantage of the cleaner emissions and lower cost of natural gas.

Because of these advantages, Favennec is seeing a big push towards developing the technology: “Everybody is working on this technology because you want to reduce your emissions, and CO2, and also have the fuel economy.”

She concedes that this push might also largely be tied to the low cost of natural gas: “If the price of the gas increases, that means all the development of these natural gas technologies maybe won’t be interesting enough [to pursue].”

There are other factors affecting the more widespread use of dual fuel technology as well. One such factor is the development of the technology. Right now, Favennec estimates the maximum percentage of natural gas in a dual fuel diesel mix to be around 60%. “If you put too much gas in the diesel engine, your fuel will ignite too early,” she explains. While the percentage increases to about 90% with a technology like HPDI (high-pressure direct injection), that technology has yet to make its way into the commercial generator industry.

Another major factor is infrastructure—how easy it will be to access natural gas. According to Favennec, the questions Canadian companies working with natural gas technologies are asking are, “When will we get better distribution with the natural gas?” and, “Do we want to invest?”

In the end, it will probably be a combination of market conditions and environmental regulations that determines the future of these fuel types. “It will always lead to two important parameters,” says Favennec. “The cost, and then the pollutants.”

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