About NGVs

What is Natural Gas?

natural-gas-chart Natural gas is a fuel typically delivered by the local gas utility company through underground pipeline distribution systems to homes, commercial/institutional facilities, factories, power plants and vehicle fueling stations. Most pipeline-supplied gas is composed of 88-95% methane, with the remainder comprising small amounts of ethane, propane and other combustible and inert gases. Natural gas is produced primarily by the decomposition of hydrocarbon-based plants and animals, and most natural gas discoveries are underground where these carbon-based materials have been trapped for thousands if not a million or more years. These underground deposits may be deep beneath the land or sea, entrained in seams of coal and/or trapped within rock deposits. More recently, advances in exploration and production technologies have unlocked the ability to extract natural gas trapped within shale rock /sediment layers. This shale gas is released through a process called hydraulic fracturing or “fracking.” Currently, shale gas accounts for about 45% of all natural gas produced in North America; most of the rest comes from conventional deep wells and a little comes from coal seams.

Some natural gas used today comes from renewable sources such as landfills, wastewater/sewage plants and agricultural facilities. This natural gas (commonly referred to as ‘biomethane’) is also produced by decomposition of hydrocarbon materials but it is not “trapped” deep in the earth. It is recoverable through gas collection systems, where it is typically “cleaned up” to remove other entrained non-desirable decomposition by-products and “concentrated” to bring it up to pipeline standards of methane and other constituent gas content.


What is CNG and LNG and How are these Different than LPG?

Compressed Natural Gas (CNG) is composed of the same natural gas that’s delivered to your home of business by the local gas utility at very low pressures (1/4psi to 2psi) but compressed to much higher pressure, usually 3600psi when dispensed to a vehicle. This is done by multi-stage compressors at the CNG station that typically run on electricity but may also be natural gas engine driven. Liquefied Natural Gas (LNG) is also the same natural gas used by millions of homes and businesses but in a liquid state, which is achieved through a cryogenic refrigeration process that drops the gas to -259°F. When refrigerated to this level, the methane and other constituent gas molecules change phase from a gas to a liquid. If allowed to warm sufficiently, the LNG will re-gasify. LNG is typically produced at a limited number of cryogenic facilities around the country, then stored in “super insulated” thermos-type vessels for use later at the production site or for transport by trucks or rail to another end-use site. The main difference between CNG and LNG is the state of the gas, although it is important to note that during liquefaction, some non-methane constituent gases “drop out” before reaching -259°F, thus LNG tends to have an even higher methane content than CNG. Although it is possible to run a light-duty vehicle on LNG (it’s been done in the past), nearly all today’s light- and medium-duty NGVs – and most heavy-duty NGVs such as Class 8 over the road trucks – run on CNG. About 1/3 of the HDVs (and some large off-road equipment, locomotives and marine vessels) run on LNG.

Liquefied Petroleum Gas (LPG) is a hydrocarbon fuel mix composed mostly of propane, with the remainder comprising other heavier hydrocarbon combustible and inert gases (‘propane” and “LPG’ are sometime used interchangeably much as ‘methane’ and ‘natural gas’ are used interchangeably, although in both cases, they are not identical). Although as gas, LPG/propane has far different properties than Natural Gas/methane. Most notably, due to molecular content, propane is heavier than air while natural gas is lighter than air… While both are used as “alternative fuels” in vehicles, they are not interchangeable.


Where does America’s Natural Gas Come From?

The US consumes about 26Trillion Cubic Feet (Tcf) of gas a year. Most of the natural gas consumed in the US – about 90% – comes from the US. Most of the rest of the natural gas consumed here comes from Canada. While the US has LNG import facilities where LNG produced elsewhere in the world may be offloaded here, the present economics of domestically produced gas have all but shut down these import facilities; some are even being modified to become export facilities. Nearly all the gas used in the lower 48 states comes from the lower 48 states and Canada. Small amounts of natural gas produced in Alaska is used there and/or liquefied and transported – again mostly to other Alaskan or arctic areas.

Two respected authorities, the U.S. Energy Information Administration (EIA) and the non-partisanPotential Gas Committee (PGC), provide reliable estimates of domestic natural gas resources. The PGC’s year-end 2012 assessment exceeds all others in their 48 year history with a reported 2,384 Tcf of technically recoverable natural gas. Combined with the U.S. DOE’s proven dry-gas reserves as of year-end 2012, the PGC estimates the U.S. has 2,722 Tcf of future supply. At the current rate of consumption in the U.S., which is about 26.8 Tcf per year, domestic natural gas resources will supply over 100 years of use.


How do NGVs Work?

Light-duty natural gas vehicles work much like gasoline-powered vehicles in that a fuel-air mixture is introduced into the engine cylinder, compressed by the piston and ignited by a spark plug. Like a gasoline vehicle, the expanding combustion gases push the cylinder down, which turns the crankshaft, which – via the rest of the powertrain – turns the wheels. Unlike a gasoline vehicle where liquid gasoline pressure is increased up to the injection pressure by the fuel pump, in a CNG fuel system, high-pressure natural gas moves from the storage tank through a regulator where its pressure is reduced to the engine’s required fuel injection system pressure. All fuels – gasoline, diesel, natural gas, ethanol, propane, alcohol (even moonshine!) – have an energy potential measured in BTUs. The engine doesn’t care – it just wants a certain amount of BTUs to ignite and create the combustion energy needed to push the piston down. NGV engines are calibrated to deliver the same amount of BTUs as gasoline so the mileage per gallon (mpg) is the same. Because CNG is a gas, we compare with gasoline by using an equivalent energy measurement – the Gasoline Gallon Equivalent (GGE)….roughly 124,800 BTUs = one GGE. To summarize, if your gasoline-fueled sedan gets 36 Hwy /26 City, your same model natural gas sedan will get equivalent mileage. Natural gas engines aren’t more efficient, they’re cleaner for the same power produced.


What’s the Difference Between “Dedicated,” “Bi-Fuel” and “Dual-Fuel” Vehicles?

Dedicated vehicles (sometimes referred to as “mono-fuel”) have only one fuel on board to run the vehicle, e.g. dedicated CNG vehicles (like the Crazy Diamond Performance™ vehicles GBT offers), have no gasoline tank and run entirely on CNG. Bi-Fuel vehicles are vehicles that are capable of running on two different fuels and – in most cases – typically only one at a time. Thus, a bi-fuel CNG-gasoline vehicle will run on the preferred fuel (usually CNG) until it runs out, then switch over to the second fuel (e.g. gasoline). Many bi-fuel vehicles will start on gasoline and run a very short time – just long enough to generate heat for the engine coolant loop — before seamlessly switching over to CNG; this is usually done to generate heat to circulate through the CNG pressure regulator to prevent the pressure drop from causing what is referred to as the Joule-Thompson effect, a physical phenomenon that produces extreme cold that could potential freeze any moisture that might be in the fuel as it passes through the regulator. Some newer “bi-fuel” vehicles actually use a small amount of gasoline while running in “CNG mode.” This is typically inly done on direct injection gasoline vehicles that also run on CNG. The short intermittent bursts of gasoline during operation are primarily to cool the gasoline injectors.

Technically, these vehicles are running in dual-fuel mode. Dual-fuel refers to the simultaneous use of two fuels in the combustion process. Dual-fuel typically refers to diesel engines that have been manufactured or retrofitted to run on both diesel fuel and natural gas at the same time, with the amount of diesel fuel displacement varying as the duty cycle varies. For example, most dual-fuel engines are diesel compression ignition engines (i.e. no spark plugs) where the vehicle starts on 100% diesel and quickly begins to displace diesel with natural gas as the call for power rises. At full throttle, e.g. when running down the highway, the proportional mix of diesel fuel / natural gas may be as high as 30% / 70%. Note that most dual-fuel engines are capable of running on only diesel if the onboard storage of natural gas runs out (not optimally, but enough to return to base of get to the next natural gas fueling location).


Where Can I Fuel a NGV?

Because vehicular natural gas (CNG of LNG) requires additional “handling” (i.e. either to compress it up to high pressure or to liquefy it), it is only available at stations specifically equipped to handle the fuel. Presently, there are about 1650 CNG stations across the US and about 125 LNG stations, most of the latter which serve heavy-duty trucks. Slightly more than one-half the CNG stations are open to the public and offer standard payment mechanisms (e.g. credit card). The number of CNG stations is growing quickly, driven by fleets’ adoption of the technology and by fuel retailers’ inclusion of CNG fueling capability at existing petroleum fuel locations such as convenience stores, highway travel plazas, truck stops and super-stores. Some fleets even elect to provide public access to their private CNG stations by installing retail dispensing capability “outside the fence.” Examples include many municipalities, transit agencies, and a number of private businesses (e.g. Waste Management’s Clean –N-Green retail CNG sites). The economics of building and operating a CNG station are typically driven by volume throughput, thus many are installed at locations convenient to an “anchor fleet” or several aggregated anchor fleets whose fuel use justifies the station investment. Many fleets whose own fuel use per year does not justify a dedicated CNG station identify a suitably convenient existing CNG station that is either nearby their home base of operations or located on a regularly traveled route.

While most NGV-driving consumers use existing public access CNG stations, some choose to install home CNG fueling appliances. These appliances compress low pressure gas delivered via local gas pipeline to their home up to 3600psi. For safety code reasons, the compressed gas is distributed directly to the vehicle’s onboard storage cylinder and not stored in a stationary vessel located at the home. At the present time, there are only one or two appliances on the market that have been tested and approved to national safety standards; several more are expected to be introduced in the near future. Generally speaking, these devices produce only a small amount of CNG per hour (0.5-1.25GGE/hr) and thus rely on the vehicle being connected at night and/or during “down-time” in order to fill the onboard cylinder. Furthermore, until production and sales of these units dramatically increases, thus providing manufacturers enough economies of scale to make these units cost competitive, these CNG appliances are expensive to buy and install. Most homeowners install these units based on environmental commitment or convenience, and not necessarily for economic reasons.


What are the Environmental Attributes and Advantages of NGVs

Methane, the primary component of natural gas, is a single carbon molecule and as such, is extremely clean burning, producing carbon dioxide and water as by-products of combustion. Natural gas is the cleanest burning alternative transportation fuel commercially available today. {Hydrogen fueled vehicles such as fiuel cell cars are cleaner but not considered commercially viable nor are there a statistically significant number of stations in use – most are demonstration projects and/or heavily subsidized fled-demo locations for a very limited number of vehicles).

The primary benefit when it comes to “new” vehicles is a reduction in NOx emissions and a reduction in greenhouse gas emissions. Depending on the particular applications and vehicles involved, the benefits may be greater or less for some pollutants. Light-duty NGVs produce approximately 16% less NOx than the newest gasoline vehicles (MY 2012 and later) and up to 95% less than older (MY2002-2007) gasoline vehicles. As a very low carbon fuel, NGVs also produce far less particulate matter (PM) than older gasoline vehicles.

More recently, greater emphasis has been placed on greenhouse gas (GHG) emissions. Natural gas contains less carbon than any other fossil fuel and thus produces fewer carbon dioxide (CO2) emissions when burned. While NGVs do emit methane, another principle greenhouse gas, the increase in methane emissions is more than offset by a substantial reduction in CO2 emissions. The California Air Resources Board (CARB) has conducted extensive analysis on this issue. CARB concludes that a CNG fueled vehicle emits 26 to 29 percent fewer GHG emissions than a comparable gasoline fueled vehicle on a well-to-wheel basis. For natural gas vehicles that run on biomethane, the GHG emissions reduction approaches 90 percent. A recent re-analysis by Argonne National Laboratories for the US EPA factored in upstream methane emissions from the natural gas production and delivery channel; it found that NGVs still produce 13-21% less GHG thans petroleum-fueled vehicles.


Are NGVs Safe?

Natural gas in an inherently safe fuel and, unlike gasoline, it dissipates into the atmosphere in the event of an unlikely accidental release because it is lighter than air. The high ignition temperature for natural gas (~1000°F compared to 495°F for gasoline and 600°F for diesel) and limited flammability range make accidental ignition or combustion of natural gas unlikely.

CNG vehicle storage cylinders and other fuel system components are manufactured to strict standards and installed in accordance with applicable codes. They are subjected to extreme testing including bonfire test, high-impact tests and bullet-fire test. CNG cylinders are built to withstand pressures 2.25 times their operating pressures. Furthermore, they are equipped with pressure relief devices that deliberately release the gas in a controlled way should the cylinder experience prolonged exposure to fire – this is a safety measure to protect firemen and other first responders. While CNG cylinders operate at 3600psi, few are aware that a child’s paintball gun operates at 5000psi or that high-pressure gases (>5000psi) such as oxygen and acetylene are routinely transported on our roads and highways every day to hospitals and industrial facilities. The industry has an excellent safety record, especially when compared to other fuel types.


Is Converting My Vehicle to CNG Legal and Will I Lose My OEM Warranty?

Converting a vehicle that was originally manufactured to run on gasoline is legal only if the retrofit (“conversion”) system is 1) EPA- or California Air Resources Board (CARB)-certified for that particular vehicle and model year, 2) installed in compliance with NFPA standards governing the safe installation of CNG systems on that vehicle. EPA-/CARB-certified systems are available through a limited number of manufacturers who have gone through the expensive and technically challenging process of engineering, testing and then submitting their vehicles to national testing laboratories for EPA/CARB compliance. These manufacturers then offer their retrofit systems through qualified installers. Despite the errant information posted on the Internet by many unscrupulous and unqualified “conversion kit” dealers, retrofitting a vehicle to run on CNG is NOT a do-it-yourself hobby. Even those with significant automotive experience MUST use an EPA-/CARB-certified system or be liable for federal penalties for “tampering with a federally approved emissions control device.” Internet kit manufacturers who claim that they are not required to have EPA or CARB certification are typically clueless to the law and its legal and liability repercussions.

If a vehicle has been properly converted to CNG using an EPA-/CARB-certified system, the OEM warranty remains in place for all items originally warranted by the OEM, except that the EPA/CARB certificate holder (manufacturer of the retrofit system) now has legal (federally imposed) responsibility for the emissions related components and systems (typically, the fuel rail, injectors, catalytic converter, etc) for the official “life of the vehicle” – this “lifetime” determination varies based on the vehicle class and type but is typically no less than 80,000 miles and often as much as 110,000 miles. In effect, the certificate provides protection to the manufacturer against “anti=-tampering” provisions of federal law but also places responsibility that was previously the OEM’s now on the retrofit system manufacturer. The installer (an agent of the manufacturer) also has responsibilities for the vehicle parts registration and tracking should there be a NHTSA-initiated recall of that vehicle.

In summary, for non-CNG related items, the OEM still must maintain the vehicle’s warranty and for those emissions-related items (including the CNG components and exhaust after-treatment system), the retrofit system manufacturer (i.e, the EPA/CARB certificate holder) must maintain the minimum federally-required warranty on those items. Furthermore, if a non-EPA-/CARB-certified system is installed, the vehicle is in violation of federal emissions anti-tampering law and also loses its OEM warranty.