Ask Joe Mechanic - CNG/LNG/LPG Vehicles

            Compressed natural gas and Propane gas are two technologies that have been well tested and with the reduction of cost of natural gas, seems to be a great alternative fuel source. A natural gas vehicle is an alternative fuel vehicle that uses compressed natural gas (CNG) or liquefied natural gas (LNG) as a cleaner alternative to other fossil fuels. Natural gas vehicles should not be confused with vehicles powered by propane (LPG), which is a fuel with a fundamentally different composition.

            As of 2009, the U.S. had a fleet of 114,270 compressed natural gas (CNG) vehicles, mostly buses; 147,030 vehicles running on liquefied petroleum gas (LPG); and 3,176 vehicles liquefied natural gas (LNG). Worldwide, there were 14.8 million natural gas vehicles by 2011.

            Existing gasoline-powered vehicles may be converted to run on CNG or LNG, and can be dedicated (running only on natural gas) or bi-fuel (running on either gasoline or natural gas. Diesel engines for heavy trucks and busses can also be converted and can be dedicated with the addition of new heads containing spark ignition systems, or can be run on a blend of diesel and natural gas, with the primary fuel being natural gas and a small amount of diesel fuel being used as an ignition source. An increasing number of vehicles worldwide are being manufactured to run on CNG. Until recently, the Honda Civic GX was the only NGV commercially available in the US market., however now Ford, GM and Ram have bi-fuel offerings in their vehicle lineup. Fords approach is to offer a bi-fuel prep kit as a factory option, and then have the customer choose an authorized partner to install the natural gas equipment.

Choosing GM's bi-fuel option sends the HD pickups with the 6.0L gasoline engine to IMPCO in Indiana to upfit the vehicle to run on CNG. Ram currently is the only pickup truck manufacturer with a truly factory-installed bi-fuel system available in the U.S. market. Outside the U.S. GM do Brazil introduced the MultiPower engine in August 2004 which was capable of using CNG, alcohol and gasoline (E20-E25 blend) as fuel, and it was used in the Chevrolet Astra 2.0 model 2005, aimed at the taxi market. In 2006 the Brazilian subsidiary of FIAT introduced the Fiat Siena Tetra fuel, a four-fuel car developed under Magneti Marelli of Fiat Brazil. This automobile can run on natural gas (CNG); 100 percent ethanol (E100); E20 to E25 gasoline blend, Brazil's mandatory gasoline; and pure gasoline, though no longer available in Brazil it is used in neighboring countries.

             NGV filling stations can be located anywhere that natural gas lines exist. Compressors (CNG) or liquifaction plants (LNG) are usually built on large scale but with CNG small home refueling stations are possible. A company called FuelMaker pioneered such a system called Phill Home Refueling Appliance (known as "Phill"), which they developed in partnership with Honda for the American GX model. Phill is now manufactured and sold by BRC FuelMaker, a division of Fuel Systems Solutions, Inc.

           

 CNG may also be mixed with biogas, produced from landfills or wastewater, which doesn't increase the concentration of carbon in the atmosphere.

            Despite its advantages, the use of natural gas vehicles faces several limitations, including fuel storage and infrastructure available for delivery and distribution at fueling stations. CNG must be stored in high-pressure cylinders (3000psi to 3600psi operation pressure), and LNG must be stored in cryogenic cylinders (-260F to -200F). These cylinders take up more space than gasoline or diesel tanks that can be molded in intricate shapes to store more fuel and use less on-vehicle space. CNG tanks are usually located in the vehicle's trunk or pickup bed, reducing the space available for other cargo. This problem can be solved by installing the tanks under the body of the vehicle, or on the roof (typical for busses), leaving cargo areas free. As with other alternative fuels, other barriers for widespread use of NGVs are natural gas distribution to and at fueling stations as well as the low number of CNG and LNG stations.

             Though LNG and CNG are both considered NGVs, the technologies are vastly different. Refueling equipment, fuel cost, pumps, tanks, hazards, capital costs are all different. One thing they share is that due to engines made for gasoline, computer controlled valves to control fuel mixtures are required for both of them, often being proprietary and specific to the manufacturer. The on-engine technology for fuel metering is the same for LNG and CNG.

            CNG, or compressed natural gas, is stored at high pressure, 3,000 to 3,600 pounds per square inch (21 to 25 MPa). The required tank is more massive and costly than a conventional fuel tank. Refueling stations are more expensive to operate than LNG stations because of the energy required for compression. Time to fill a CNG tank varies greatly depending on the station. Home refuelers typically fill at about 0.4 GGE/hr. "Fast-fill" stations may be able to refill a 10 GGE tank in 5–10 minutes. Also, because of the lower energy density, the range on CNG is limited by comparison to LNG.

            LNG, or liquified natural gas, is natural gas that has been cooled to a point that it is a cryogenic liquid. In its liquid state, it is still more than 2 times as dense as CNG. LNG is dispensed from bulk storage tanks at LNG fuel stations at rates exceeding 20 GGE/min. Because of its cryogenic nature, it is stored in specially designed insulated tanks. Generally speaking, these tanks operate at fairly low pressures (about 70-150 psi) when compared to CNG. A vaporizer is mounted in the fuel system that turns the LNG into a gas (which may simply be considered low pressure CNG).

            LNG – and especially CNG – tends to corrode and wear the parts of an engine less rapidly than gasoline. Thus it's quite common to find diesel engine NGVs with high mileages (over 500,000 miles). Emissions are cleaner, with lower emissions of carbon and lower particulate emissions per equivalent distance traveled. There is generally less wasted fuel. CNG-powered vehicles are considered to be safer than gasoline-powered vehicles.

            Autogas, also known as LPG, has different chemical composition, but still petroleum based gas, has a number of inherent advantages and disadvantages, as well as noninherent ones. The inherent advantage of autogas over CNG is that it requires far less compression (20% of CNG cost), is denser as its a liquid at room temperature, and thus far cheaper tanks (consumer) and fuel compressors (provider) than CNG. As compared to LNG, it requires no chilling (and thus less energy), or problems associated with extreme cold such as frostbite. Like NGV, it also has advantages over gasoline and diesel in cleaner emissions, along with less wear on engines over gasoline. The major drawback of LPG is its safety, the fuel is heavier than air, which causes it to collect in a low spot in the event of a leak, making it far more hazardous to use, as more care is needed.

            Varieties of LPG bought and sold include mixes that are primarily propane (C3H8), primarily butane (C4H10) and, most commonly, mixes including both propane and butane, depending on the season — in winter more propane, in summer more butane In the United States, primarily only two grades of LPG are sold, commercial propane and HD-5. The Gas Processors Association (GPA) and the American Society of Testing and Materials (ASTM) publish these specifications. Propane/butane blends are also listed in these specifications. Propylene, butylenes and various other hydrocarbons are usually also present in small concentrations. HD-5 limits the amount of propylene that can be placed in LPG, and is utilized as an autogas specification. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. In the United States, tetrahydrothiophene (thiophane) or amyl mercaptan are also approved odorants, although neither is currently being utilized.

           

LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. Dr. Walter Snelling first produced it in 1910, and the first commercial products appeared in 1912. It currently provides about 3% of all energy consumed, and burns relatively cleanly with no soot and very few sulfur emissions. As it is a gas, it does not pose ground or water pollution hazards, but it can cause air pollution. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel oil and 43.5 MJ/kg for premium grade petrol (gasoline). However, its energy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as its relative density is lower (about 0.5—0.58, compared to 0.71—0.77 for gasoline).

           

In places like the US, Thailand, and India, there are five to ten times more stations thus making the fuel more accessible than NGV stations. Other countries like Poland, South Korea, and Turkey, LPG stations and autos are widespread while NGVs are not. In addition, in some countries such as Thailand, the retail LPG fuel is considerably cheaper in cost.        Though ANG (adsorbed natural gas) has not yet been used in either providing neither stations nor consumer storage tanks, its low compression (500psi vs 3600 psi) has the potential to drive down costs of NGV infrastructure and vehicle tanks.

 

The primary component of natural gas is methane (CH₄), the shortest and lightest hydrocarbon molecule. It may also contain heavier gaseous hydrocarbons such as ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀), as well as other gases, in varying amounts. Hydrogen sulfide (H₂S) is a common contaminant, which must be removed prior to most uses. Combustion of one cubic meter yields 38 MJ (10.6 kWh). Natural gas has the highest energy/carbon ratio of any fossil fuel, and thus produces less carbon dioxide per unit of energy.

            The major difficulty in the use of natural gas is transportation. Natural gas pipelines are economical and common on land and across medium-length stretches of water (like Langeled, Interconnector and Trans-Mediterranean Pipeline), but are impractical across large oceans. Liquefied natural gas (LNG) tanker ships, railway tankers, and tank trucks are also used.

            CNG is typically stored in steel or composite containers at high pressure (3000 to 4000 psi, or 205 to 275 bar). These containers are not typically temperature controlled, but are allowed to stay at local ambient temperature. There are many standards for CNG cylinders; the most popular one is ISO 11439. For North America the standard is ANSI NGV-2.

           

LNG storage pressures are typically around 50-150 psi, or 3 to 10 bar. At atmospheric pressure, LNG is at a temperature of -260°F (-162°C), however, in a vehicle tank under pressure the temperature is slightly higher (see saturated fluid). Storage temperatures may vary due to varying composition and storage pressure. LNG is far denser than even the highly compressed state of CNG. As a consequence of the low temperatures, vacuum insulated storage tanks typically made of stainless steel are used to hold LNG.

           

CNG can be stored at lower pressure in a form known as an ANG (Adsorbed Natural Gas) tank at 35 bar (500 psi, the pressure of gas in natural gas pipelines) in various sponge like materials, such as activated carbon and metal-organic frameworks (MOFs). The fuel is stored at similar or greater energy density than CNG. This means that vehicles can be refueled from the natural gas network without extra gas compression; the fuel tanks can be slimmed down and made of lighter, less strong materials.

           

As its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurized steel vessels. They are typically filled to between 80 percent and 85 percent of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapor pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (32 psi) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (320 psi) for pure propane at 55 °C (131 °F). LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. There are two main dangers from this. The first is a possible explosion if the mixture of LPG and air is within the explosive limits and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration. In addition, an odorant is mixed with LPG used for fuel purposes so that leaks can be detected more easily.

           

Conversion kits for gasoline or diesel to LNG/CNG are available in many countries, along with the labor to install them. However, the range of prices and quality of conversion vary enormously. Recently, regulations involving certification of installations in USA has been loosened to include certified private companies, those same kit installations for CNG have fallen to the $6,000+ range (depending on type of vehicle).

           

With the recent increase in natural gas production due to widespread use of fracking technology, many countries, including the United States and Canada, now can be self-sufficient. Canada is a substantial net exporter of natural gas, though the United States still has a net import of natural gas. Natural gas prices have decreased dramatically in the past few years and are likely to decrease further as additional production comes on line. However, the EIA predicts that natural gas prices will start increasing in a few years as the most profitable natural gas reserves are used up. Natural gas prices have decreased from $13 per mmbtu (USD) in 2008 to $3 per mmbtu (USD) in 2012. It is likely therefore that natural gas-powered vehicles will be increasingly cheaper to run relative to gasoline-powered vehicles. The issue is how to finance the purchase and installation of conversion kits. Some support may be available through the Department of Energy. Private initiatives, which essentially lease the conversion equipment in exchange for slightly higher natural gas refueling, can be self-financing and offer considerable advantages to liquidity strapped consumers.

           

Natural Gas has been used as a motor fuel in Canada for over 20 years.^{http://en.wikipedia.org/wiki/Natural_gas_vehicle - cite_note-36} With assistance from federal and provincial research programs, demonstration projects, and NGV market deployment programs during the 1980s and 1990s, the population of light-duty NGVs grew to over 35,000 by the early 1990s. This assistance resulted in a significant adoption of natural gas transit buses as well. The NGV market started to decline after 1995, eventually reaching today’s vehicle population of about 12,000.

            This figure includes 150 urban transit buses, 45 school buses, 9,450 light-duty cars and trucks, and 2,400 forklifts and ice-resurfacers. The total fuel use in all NGV markets in Canada was 1.9 petajoules (PJs) in 2007 (or 54.6 million litres of gasoline litres equivalent), down from 2.6 PJs in 1997. Public CNG refueling stations have declined in quantity from 134 in 1997 to 72 today. There are 22 in British Columbia, 12 in Alberta, 10 in Saskatchewan, 27 in Ontario, and 1 in Québec. There are only 12 private fleet stations.

            As of December 2009, the U.S. had a fleet of 114,270 compressed natural gas (CNG) vehicles, 147,030 vehicles running on liquefied petroleum gas (LPG), and 3,176 vehicles running on liquefied natural gas (LNG). The NGV fleet is made up mostly of transit buses but there are also some government fleet cars and vans, as well as increasing number of corporate trucks replacing diesel versions, most notably Waste Management, Inc and UPS trucks. As of 12-Dec-2013 Waste Management has a fleet of 2000 CNG Collection trucks; as of 12-Dec-2013 UPS has 2700 alternative fuel vehicles. As of February 2011, there were 873 CNG refueling sites, 2,589 LPG sites, and 40 LNG sites, led by California with 215 CNG refueling stations in operation, 228 LPG sites and 32 LNG sites. The number of refueling stations includes both public and private sites, and not all are available to the public. As of December 2010, the U.S. ranked 6th in the world in terms of number of NGV stations.

            When LPG is used to fuel internal combustion engines, it is often referred to as autogas or auto propane. In some countries, it has been used since the 1940s as a petrol alternative for spark ignition engines. In some countries, there are additives in the liquid that extend engine life and the ratio of butane to propane is kept quite precise in fuel LPG. Two recent studies have examined LPG-fuel-oil fuel mixes and found that smoke emissions and fuel consumption are reduced but hydrocarbon emissions are increased. The studies were split on CO emissions, with one finding significant increases, and the other finding slight increases at low engine load but a considerable decrease at high engine load. Its advantage is that it is non-toxic, non-corrosive and free of tetraethyllead or any additives, and has a high octane rating (102-108 RON depending on local specifications). It burns cleanlier than petrol or fuel oil and is especially free of the particulates from the latter.

           

            LPG has a lower energy density than either petrol or fuel oil, so the equivalent fuel consumption is higher. Many governments impose less tax on LPG than on petrol or fuel oil, which helps offset the greater consumption of LPG than of petrol or fuel oil. However, in many European countries this tax break is often compensated by a much higher annual road tax on cars using LPG than on cars using petrol or fuel oil. Propane is the third most widely used motor fuel in the world. 2008 estimates are that over 13 million vehicles are fueled by propane gas worldwide. Over 20 million tons (over 7 billion US gallons) are used annually as a vehicle fuel.

            Not all automobile engines are suitable for use with LPG as a fuel. LPG provides less upper cylinder lubrication than petrol or diesel, so LPG-fueled engines are more prone to valve wear if they are not suitably modified. Many modern common rail diesel engines respond well to LPG use as a supplementary fuel. This is where LPG is used as fuel as well as diesel. Systems are now available that integrate with OEM engine management systems.

            The recent increases in natural gas production in the United States, now number one in the world in CNG production, makes looking at this technology extremely attractive. Commercial fleets are increasingly looking at conversion to natural gas, with the biggest movement now being explored is in the commercial trucking industry. With tighter regulations on commercial diesel emissions, CNG appears to be the answer being explored the most and expect to see major changes over the next few years. If this conversion is successful, which appears highly likely, heavy truck emissions would be cut significantly.

            Next week we will wrap up the discussion on alternative fuels. Some information for this article obtained from Wikipedia.org.

This week’s recalls:

1,176,407 008-2013 Buick Enclave and GMC Acadia and 2009-2013 Chevrolet Traverse and 2008-2010 Saturn Outlook vehicles.
In the affected vehicles, increased resistance in the driver and passenger seat mounted side impact air bag (SIAB) wiring harnesses may result in the SIAB and seat belt pretensioners not deploying in the event of a crash. Failure of the side impact air bags and seat belt pretensioners to deploy in a crash increases the risk of injury to the driver and front seat occupant.

303,013 009-2014 Chevrolet Express and GMC Savana vans manufactured January 27, 2009, through March 7, 2014.
With a gross vehicle weight rating of 10,000 pounds and less and equipped with front passenger air bags. In the affected vehicles, during a frontal impact below the air bag deployment threshold, if an unbelted front passenger's head hits the instrument panel above where the passenger air bag is located, the panel may not sufficiently absorb the impact. As such, these vehicles fail to meet the requirements of Federal Motor Vehicle Safety Standard number 201, "Occupant Protection in Interior Impact." In the event of a crash below the air bag deployment threshold, an unbelted front passenger seat occupant has an increased risk of injury.

63,903 2013-2014 Cadillac XTS vehicles manufactured February 14, 2012, through March 7, 2014.
In the affected vehicles, a cavity plug on the brake booster pump connector may dislodge allowing corrosion of the brake booster pump relay connector. The corrosion of the brake booster pump relay connector may cause a resistive short and melt the connector, increasing the risk of a fire.

886,815 Honda is recalling certain 2005-2010 Honda Odyssey vehicles manufactured June 23, 2004, through September 4, 2010.
In the affected vehicles, the fuel pump strainer cover may deteriorate allowing fuel to leak out. A fuel leak increases the risk of a fire.

18,092 2014 Fiat 500L vehicles manufactured April 5, 2013, through January 22, 2014.

In certain temperatures, moving the transmission shift lever may have a delayed effect or no effect on selecting a transmission gear. If there is no effect, the vehicle might not shift out of the Park position. If there is a delayed effect, the vehicle may move in an unintended or unexpected direction, increasing the risk of a crash.

18,690 2012-2013 Dodge Durango and Jeep Grand Cherokee vehicles manufactured October 11, 2011, through October 1, 2012.
Under certain braking events, the Ready Alert Braking System (RAB) may result in the driver experiencing a hard brake pedal feel. If the driver experiences a hard brake pedal, the driver may not push the pedal as intended, lengthening the distance needed to stop the vehicle and increasing the risk of a crash.

If you own one of these affected vehicles, contact your dealer or the manufacturer for further instructions.