What Kind Of Fuel Do Electrical Generators Need?

Today’s electrical generators are available in many different fueling options. Diesel generators are the most popular industrial generators on the market. Residential generators more commonly include: natural gas generators or propane generators, while the smaller portable generators typically run on gasoline, diesel fuel, or propane. Some generators are bi-fuel capable – running on both gasoline and diesel.

Generator Fuel Tanks

The fuel system ensures the generator has the necessary raw materials needed to provide electricity by initiating the internal combustion process. Without fuel, combustion can’t take place and the generator can’t convert the mechanical energy created into electrical energy. Generator fuel needs to be stored on-site so the generator can be put into operation immediately when necessary.

Depending on the type of generator and its application, fuel tanks may be mounted to the generator frame or they may be external tanks located far from the actual generator. In general, the bigger the generator and the longer it needs to run, the bigger the fuel tank. Generator fuel is stored in tanks of various capacities, depending on the intended use of the generator and the amount of power required. Tanks my be located above ground, below ground, or sub base. Sub base tanks are intended for storing less than 1,000 gallons of fuel and are located above ground, but below the base of the generator set.

Above ground and below ground generator fuel storage tanks are a better choice for high capacity needs. Underground storage tanks are more expensive to install, but they tend to last longer since they are protected from the elements. There are pros and cons to both types of fuel storage tanks but you won’t be alone in making a decision. Generator fuel tanks and generator fuel systems must meet several code requirements and approvals before they can be installed, whether the installation is for residential or commercial use.

The primary code governing generator fuel tanks in the United States is the National Fire Protection Association Codes and Standards (NFPA), particularly sections NFPA 30 and NFPA 37. As such, all requests for a generator fuel tank must be submitted to the State Fire Marshall for approval.

To determine your minimum fuel tank capacity needs, you’ll need to think about how you intend to use the generator. For short or infrequent power outages, a backup generator with a smaller storage tank may be acceptable, however you’ll need to refill the tank more frequently than you’d have to refill larger tanks. Larger storage tanks may be required if you’re planning to power a large commercial facility with a prime generator or if you are subject to long, frequent power outages.

Your generator supplier can help you determine the optimal fuel tank size to ensure you have enough fuel on hand when you need it. One more thing to keep in mind both when buying a generator and selecting a generator fuel storage tank is the cost and availability of the fuels to your location. It’s a good idea to talk to local fuel suppliers before you buy a generator to get a better idea of the cost and logistics involved in obtaining generator fuel.

Generator Exhaust Systems and Emissions Controls

As machines that burn fossil fuels and run continuously, even if that run time is erratic, generators must be equipped with components to cool them off and to filter emissions. Generator cooling and ventilation systems reduce and remove heat in a variety of ways:

Water. Water can be used to cool off generator components. This type of coolant system is typically limited to specific situations or very large units of 2,250 kW and higher.
Hydrogen. Hydrogen is a very efficient coolant that is used to absorb heat given off by a running generator. The heat is transferred to a heat exchanger and a secondary cooling circuit, often located in large, on-site cooling towers.
Radiators and fans. Smaller generators are cooled through a combination of a standard radiator and fan.

The fumes emitted by generators are just like the exhaust given off by other gas or diesel powered engines. They include toxic chemicals, like carbon dioxide, which must be filtered and removed from emissions. The generator exhaust system manages this task.

Exhaust pipes are connected to the engine where they direct fumes up, out, and away from the generator and the facility. The pipe extends outside the building housing the generator and should terminate far away from doors, windows, and other areas of air intake.

In addition to exhaust systems, some generators are subject to federal emission controls. The generator emissions monitored are: Nitrogen Oxide (NOx), Hydrocarbons, Carbon Monoxide (CO), and Particulate Matter.

In general, emergency generators and generators that run for less than 100 hours per year are not subject to federal generator emissions requirements, however, permanently installed prime generators and standby generators are subject to federal emissions requirements under three EPA rules:

National Emission Standard for Hazardous Air Pollutants (NESHAP) – For Reciprocating Internal Combustion Engines (RICE). 40 Code of Federal Regulations Part 63, Subpart ZZZZ. Also known as the RICE rule.
New Source Performance Standards (NSPS) – Standards of performance for stationary spark ignition engines. 40 CFR, Part 60, Subpart JJJJ. Also known as the spark ignition NSPS rule.
Standards of Performance for Stationary Compression Ignition Internal Combustion Engines. 40 CFR, Part 60, Subpart IIII. Also known as the compression Ignition NSPS rule.

The good news is that many newer gensets already meet generator emissions standards thanks to manufacturing improvements. Older gensets may be grandfathered in, making them exempt from federal regulations, and subject only to state and local emissions standards. Emissions control requirements vary by manufacturer, generator size, and production date so the best way to determine your emissions requirements is to talk to your generator dealer or manufacturer.

For a deeper look at emission regulations, read this white paper from Cummins, “The Impact of Tier 4 Emission Regulations on the Power Generation Industry”.