By Mike McGlothlin
For decades, diesel generators have been the go-to for both primary and stand-by power generation. However, thanks to their lower emissions output, lower purchase price in most instances and fuel costs, industrial and commercial-grade natural gas gen-sets have become increasingly popular in recent years. Here, we’ll explore the advantages of diesel and natural gas generators, as well as their drawbacks. Along the way, we’ll also spell out the key differences between each type of power generation.
Benefits At A Glance: Diesel Generators
*More energy dense fuel source
*Greater fuel efficiency
*Low rpm, high durability
*Better load response/recovery time
*Low maintenance
Benefits At A Glance: Natural Gas Generators
*Cleaner emissions
*Quiet operation
*Cheaper fuel source
*Zero fuel storage requirements
*Usually more affordable
Diesel Gen-Sets And Natural Gas Gen-Sets Both Have Their Place
Before any advantages and disadvantages between diesel and natural gas are discussed, it’s worth noting that either form of power generation can make sense depending on your specific application and needs. Different operating conditions, power requirements, or operating environments can make one fuel source a better option than the other. As a general rule of thumb, diesel powered generators are the most common portable choice, while natural gas gen-sets are typically stationary given their utility hookup, along with being cheaper to refuel. But this is only the tip of the iceberg, as budget, fueling requirements and concerns, emissions, noise, and size all factor into most industrial generator decisions.
Diesel Advantage #1: Age-Old, Proven Engine Technology
An internal combustion process that uses compressed air to initial combustion rather than spark
plugs (i.e. compression ignition) makes a diesel engine inherently simpler, and low maintenance and reliability are some of its most pronounced advantages. Add in the fact that many industrial-grade diesel engines boast large main and rod bearings, forged steel hard-parts, overkill head-to-block fastening, and operate at relatively low rpm and you can see why diesel generators typically enjoy such long service lives. But perhaps more importantly, diesel engines respond more favorably when placed under load, with their “load response” (or recovery) known to be much quicker than that of a natural gas generator.
Diesel Advantage #2: More Fuel Efficient & Less Hazardous
With diesel fuel being considerably more energy dense than natural gas (think higher BTU content), it stands to reason that diesel-powered generators consume less fuel. In fact, a diesel is between 20 and 40-percent more fuel efficient, depending on the specific engine. This means it can run for longer periods of time without the need to refuel, ideal for continuous operation. On top of that, diesel engines are more efficient under high loads, which is often the case in stand-by applications where ‘round the clock run-time is required at 90-percent (or higher) load. As an oil-based fuel, diesel is also much less volatile than natural gas, making it the safer fuel source for power generation.
Diesel Disadvantage #1: Emissions & NVH
While diesel is the best choice for optimum fuel efficiency, engine longevity, and safety, if you’re concerned about emissions, it might not be a perfect fit for you and your operation. On average, diesel generators produce 30-percent more nitrogen oxide (NOx), carbon dioxide (CO2), and sulfur oxide (SOx) emissions than natural gas generators. Diesels also emit significantly more particulate matter (PM), along with an unmistakable, distinct odor. In the way of noise, vibration, and harshness (NVH), diesel gen-sets take the lead, too, although much of it can be dampened thanks to today’s state-of-the-art sound-attenuating enclosures.
Diesel Disadvantage #2: Mandatory Fuel Maintenance
We already explained that diesel is a much safer fuel source than natural gas, and that’s true, but the fuel that feeds a diesel engine requires regular attention. Diesel is naturally attracted to water at the molecular level (and can even absorb it), so routine fuel filter and water separator replacements must be observed. But that’s only the beginning. Diesel fuel can begin to degrade within weeks of being produced at the refinery. This means any fuel being stored for stand-by use must either be treated for long-term stability or rotated out during scheduled generator exercising. Finally, there is the question of space. Beyond what common belly tanks provide, stored fuel (sometimes skid-mounted tanks) can take up considerable real estate.
Natural Gas Advantage #1: Cleaner Emissions
CO2 Icon. Emissions Reduction of Carbon Gas. Black Cloud of CO2 Gas. Decrease Pollution Icon. Carbon Dioxide Emissions. Vector illustration.
One of the biggest selling points of natural gas generators boils down to their superior cleanliness over diesel. As you’ve likely deduced from earlier reading, natural gas generators produce approximately 30-percent less nitrogen oxide (NOx), carbon dioxide (CO2), and sulfur oxide (SOx) pollutants. They also emit far less in the way of particulate matter (PM) than diesel
generators—somewhere around 90-percent less. This is because gaseous fuels, which are made up of microscopic, readily combustible molecules that burn off in a nearly complete manner, inherently produce very little PM. An added benefit is that, unlike diesel generators, there is also no strong odor associated with the operation of a natural gas generator.
Natural Gas Advantage #2: Affordable & Feasible
The price of natural gas is often half the going price for diesel fuel, which obviously makes natural gas the cheaper fuel source. Also consider the obvious refueling convenience… Thanks to being directly integrated into a pipeline, there is no need for fuel to be trucked in or space consumed for fuel storage. Unlike diesel fuel, natural gas requires little to no attention, as the gas won’t break down and potentially damage equipment or lead to poor performance. When considering the overall cost(s) associated with a natural gas generator, they’re typically more affordable than diesel, especially in for 150kW and lower units.
Natural Gas Disadvantage #1: Less Efficient, Highly Volatile Fuel
One point to be clear on is that, while natural gas is highly cost-effective as a fuel and is often half the price of diesel, a natural gas generator is far less fuel efficient than a diesel generator. This is because the energy density of natural gas is, on average, 30-percent lower than diesel. Unlike diesel fuel, natural gas is made up of 90-percent methane, which makes it exceptionally volatile, especially if it’s exposed to air. If the right amount of oxygen mixes with natural gas, virtually any type of ignition source (not even excluding turning on a light switch) can set it off. This makes a natural gas leak extremely dangerous.
Natural Gas Disadvantage #2: Dependency On The Pipeline
Being connected to a dedicated natural gas pipeline definitely has its upsides—with no fuel storage requirement, low cost, and reduced emissions being among them—but during a natural disaster or significant weather event its supply can become disrupted. In environments such as police stations, firehouses, and especially hospitals, where the use of critical equipment, communication, and lighting can’t be interrupted, stand-by power is almost exclusively provided by diesel generators. While widespread emergencies can also make delivery of diesel fuel difficult (or even impossible), being dependent on a natural gas generator during a prolonged outage is a scenario that pushes most buyers toward diesel power generation.
Natural Gas Disadvantage #3: Less Longevity, Larger In Size
Though the internal makeup of an engine running on natural gas may not differ much from what you’ll find inside a diesel engine, natural gas engines typically have a shorter service life. Nitration, oxidation, and water contamination are all common issues found in natural gas engine oils. Of course, with spark plugs, coils, and/or a carburetor to inspect, trouble shoot, and periodically replace, the maintenance requirements of a natural gas generator are more extensive than they are on a diesel generator. Then come the overall dimensions. On average, a natural gas generator is notably larger in height, width, and length than a comparable diesel version.
