Most generators supporting data centers tend to use diesel as the fuel source, as the fuel can be stored on site to be controlled and replenished. The amount of filtering of the fuel can vary, as the diesel that is filled into a truck might seem reliably clean, but the truck tank or fuel lines used may have been used for other types of fuel and have residual contaminants. Water, machinery oil, and other liquids can contaminate the fuel even before arrival, which can significantly lower fuel efficiency and even damage the generator engines.
Since typical data center diesel generators are sitting in standby mode and tested for only a limited number of hours per year, the fuel has been sitting in storage and can get stale and have algae and water build up. Additives can be used to prevent diesel fuel issues but for most a dedicated fuel filtering system and maintenance program helps to ensure better quality fuel and reduce variability in the energy content.
Depending on the region or country the challenge can be not only on the quality of the fuel but the quantity. Developing countries rely on diesel fuel to operate many of their infrastructure needs and knowing that a data center might be sitting with thousands of gallons of fuel means that they might be the last to be replenished, for the sake of electricity, transportation or the economy. Once that fuel has finally been delivered it may not be from the best source and should be filtered and tested.
A spectrometry test of the fuel can find out whether kerosene or other oils have been blended with the diesel as well as determine the energy content. Multistage filters and centrifuges are used to reduce as much of the contaminants as possible before adding to the storage tanks or to be used by the generators. Another step of filtration and separation happens at the generator as the fuel is drawn into the engine. With sensors to measure the pressure on each side of the fuel filtration system, the filters can be changed when needed rather than by runtime hours to catch issues that may reduce uninterrupted runtime.
Natural gas is an upcoming solution for long-term data centers and campuses, where the designers and owners have been keen to plan for the pipelines. And of those installed, almost half can burn more than natural gas, including fuel gas from oil fields, coal mine gas, synthetic gas, landfill gas, and a variety of biogases. The challenge has been on the environmental side, as there are stringent emission requirements that must be followed or risk penalties that could lead to suspending the generator plant.
When the commissioning agents are going over the gas generators, they can validate the factory calibration but then often need to adjust according to the actual energy capacity of the fuel. While natural gas may be the basis, biogas might achieve half of the energy content, with syngas and others being 10-20% of natural gas. The manufacturers have stepped up to make gas-fueled engines that can run on a variety of fuels with immensely different energy content. To do this, the generator controls are sensing the outdoor conditions to calculate how temperature, humidity and pressure of the air can predict the performance of the fuel with the engine, then adjust the air needed for combustion to optimize the system.
Constant monitoring of the fuel gas is required, as methane gas from landfills, anaerobic digestors and coal mines can change over time. Natural gas from a utility can be much less variable as well as reliable, as evidenced by systems that kept facilities running during hurricane Sandy. And overall those in the data center industry, like the utility industry, prefer equipment that is reliable and durable which can yield lower maintenance intervals.