Natural gas and diesel are prominent fuel sources for vehicles and industrial applications. Diesel, a traditional petroleum-based fuel, has long been a workhorse for heavy-duty transportation and machinery due to its energy density and widespread availability. Natural gas, composed primarily of methane, has emerged as an alternative, utilized in both compressed (CNG) and liquefied (LNG) forms.
Environmental Footprint
Natural gas generally offers environmental advantages over diesel due to its cleaner combustion properties. Natural gas combustion produces lower levels of particulate matter (PM) compared to diesel because it burns more completely, leading to significantly reduced soot emissions.
Natural gas also yields lower emissions of nitrogen oxides (NOx) and sulfur oxides (SOx). Natural gas is inherently very low in sulfur, resulting in virtually no SOx emissions, unlike diesel which still produces some. While both fuels produce NOx, natural gas vehicles often require less complex aftertreatment systems to meet stringent NOx emission standards. Some studies indicate natural gas engines can achieve up to 80% less nitrogen oxide emissions compared to diesel.
Regarding greenhouse gas emissions, natural gas typically offers a 20-30% reduction in carbon dioxide (CO2) compared to diesel. The use of renewable natural gas (RNG), derived from organic waste, can further reduce greenhouse gas emissions by capturing methane that would otherwise be released into the atmosphere, potentially achieving sub-zero emissions.
Economic Implications
Economically, natural gas and diesel differ in fuel, vehicle acquisition, and maintenance costs. Fuel prices for natural gas have historically been lower and more stable compared to diesel, which is often subject to global market fluctuations. For instance, in one period, the national average price of compressed natural gas (CNG) was $2.99 per diesel gallon equivalent, while diesel was $4.25 per gallon, potentially saving fleets thousands annually.
However, the initial purchase cost of natural gas vehicles (NGVs) is typically higher than comparable diesel vehicles. NGVs can cost between $30,000 to $50,000 more due to specialized fuel tanks, robust fuel lines, and specific engine modifications. Government incentives are often available to help offset these costs.
Overall maintenance costs for NGVs can be slightly higher than diesel vehicles, though natural gas engines generally have simpler aftertreatment systems. Diesel engines, while generally having longer lifespans, can incur more expensive repairs, particularly for their complex high-pressure fuel injection systems. Natural gas engines, burning cleaner fuel, may experience longer intervals between oil changes and reduced carbon buildup, contributing to lower routine maintenance needs.
Operational Characteristics
Operationally, natural gas and diesel vehicles differ in engine performance, fuel storage, refueling infrastructure, and range. Natural gas engines offer performance comparable to diesel engines in terms of horsepower, acceleration, and cruise speed. A notable difference is that natural gas engines typically run quieter than their diesel counterparts, often by up to 10 decibels.
Compressed natural gas (CNG) is stored in high-pressure cylindrical tanks, which are often heavier and bulkier than liquid diesel tanks, potentially reducing cargo capacity. Liquefied natural gas (LNG) offers higher energy density than CNG, allowing for more fuel storage in a smaller volume, though it requires cryogenic tanks and specialized handling. Diesel, being a liquid, is stored in conventional tanks, which are generally more space-efficient.
Refueling infrastructure for natural gas is less widespread than for diesel. As of 2023, the United States had over 700 public CNG fueling stations and approximately 50 LNG stations, predominantly serving long-haul trucking. This contrasts sharply with the extensive network of diesel stations available nationwide. Many natural gas fleets invest in private, on-site fueling infrastructure to ensure convenient access, though this requires a significant initial investment.
The driving range of natural gas vehicles is generally less than that of comparable diesel vehicles due to the lower energy density of natural gas, especially CNG. While LNG offers a range more comparable to conventional fuels, CNG vehicles may require more frequent refueling stops. For instance, a natural gas truck might have a range of just over 200 miles with a 49.8 diesel gallon equivalent capacity.