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"  Natural gas has been used in our homes for generations. Americans use it to run water heaters, home furnaces, stoves, clothes dryers, and other appliances. As a fuel it accounts for 24 percent of our total energy consumption nationwide, all but 1 percent in residential applications. And as we reported last fall (&amp;quot;Drilling Down,&amp;quot; September 2011), new fracking techniques are tapping domestic reserves that previously were not economically viable. Vast global supplies are projected to last well into the next century even if natural gas replaces gasoline completely. So it should be no surprise that natural gas will remain incredibly cheap. It runs at one-half to one-third the current cost of gasoline on an energy-equivalent measure. In a properly tuned engine, natural gas combustion delivers 20 percent lower carbon emissions and about a 25 percent reduction in greenhouse gases compared with the cleanest gasoline engines, all without damaging existing catalytic converter systems. So right about now you&amp;#039;re probably wondering: Why aren&amp;#039;t we putting this stuff in our cars?  As it turns out, there are very few technological barriers to overcome. In fact, converting existing vehicles to burn natural gas isn&amp;#039;t particularly challenging. Unfortunately, if you tried to do it yourself, you&amp;#039;d more than likely run afoul of the Clean Air Act&amp;#039;s rules against modifying fuel systems--a violation that could cost you up to $5000 in fines for every day you drive the converted vehicle. So if you want to green your wheels today, the only way to do it is by hiring a certified compressed-natural-gas (CNG) installer to do the job. To get the skinny on aftermarket CNG systems, I visited NatGasCar in Cleveland. It&amp;#039;s a startup shop that augments gasoline cars by installing a parallel natural gas fuel system. They showed me their latest creation, a dual-fuel Dodge Caravan intended for airport taxi service. It starts on gasoline and switches over to natural gas once the engine warms up. NatGasCar&amp;#039;s biggest component is also its most crucial and expensive--the compressed-natural-gas fuel tank situated behind the rear seats in the cargo area. The company uses a Type 4 tank, the most advanced kind. It reduces weight with a plastic composite core wrapped in carbon fiber and is rated for severe impact and puncture resistance.  Between the tank and the engine is the fuel regulator, which reduces the fuel-tank pressure of 3600 psi to a usable 125 psi delivered to the engine. The fuel regulator is heated to prevent freezing from the expansion of the gas. The lower-pressure gas travels to the engine, Chrysler&amp;#039;s flex-fuel-capable Pentastar V-6. A flex-fuel engine is important, since it has hardened valves and valve seats, which are necessary for CNG operation. The natural gas is routed through a parallel fuel rail, and a second set of injectors is plugged into a clever adapter designed to accommodate both the gasoline and CNG injectors on the same injection port. Natural gas runs at an ideal air--fuel ratio of about 16.8:1, whereas gasoline runs happily at 14.6:1 for the Pentastar engine. As a result, the programming for the new injectors has to be slightly different. NatGasCar&amp;#039;s wiring harness intercepts the signals from the engine-control module and, depending upon which fuel is selected, turns on either the gasoline or the CNG injectors. The signals bound for the gasoline injectors are modified to deliver the appropriate amount of fuel to the natural gas injectors. This way, very little fine tuning is necessary, and the car&amp;#039;s engine-control unit does most of the work. Fueling Woes So a new fuel tank and a little bit of tinkering with the fuel injectors and I&amp;#039;m ready to go, right? Unfortunately not. Natural gas is delivered across the country to millions of homes. But what would seem to be the ideal distribution network is actually the biggest headache of natural gas vehicles. Home natural gas is delivered at about 0.5 psi, but natural gas in vehicles needs to be pressurized to 3600 psi. So if you want to use CNG in your car, you&amp;#039;ll need a compressor. A National Fire Protection Association safety standard bans compressed gas storage in homes, so a stand-alone multistage compressor pump in the garage must be hooked up to the vehicle&amp;#039;s fuel tank, filling it directly. This leads to fueling times of up to 22 hours (even longer than equivalent home charging times for electric vehicles). Honda&amp;#039;s Civic Natural Gas is paired with a home compressor system called Phill ($4500), the only commercially available product of its kind. NatGasCar is developing a compressor system capable of 8-hour fill-ups; the current target price is $3500. Some states have incentivized the installation of high-speed filling systems at gas stations, where fill times are as brief as 4 to 5 minutes, much like gasoline&amp;#039;s. But these systems cost $750,000 per station to install, and low demand means there are only 941 high-pressure CNG filling stations scattered across the country, mostly in New York, California, Utah, and Texas. Economics Okay, okay, it&amp;#039;s a pain to fuel CNG vehicles, but is it worth it? Nationwide, natural gas ranges from 79 cents to $1.50 for a gasoline gallon equivalent (gge) of fuel. That&amp;#039;s considerable savings over petroleum-based products, especially considering that CNG vehicles get the same or better relative fuel economy per Btu because of the higher octane rating of natural gas. Our test drives indicated no hit to performance, and a perfectly acceptable range of about 250 miles. But there are some pretty extraordinary initial setup costs. A properly installed conversion will run anywhere from $6500 for a basic system to $12,000 for a top-of-the-line installation with a high-capacity, composite fuel tank. If you want a home fueling compressor, tack on another $3500 minimum. Even at the low end, you&amp;#039;re looking at spending enough on the conversion to buy more than 1800 gallons of gasoline at today&amp;#039;s prices. Those prices will ultimately determine the fate of CNG vehicles. High gasoline prices historically have caused furious investment in cheaper, cleaner fuels, followed by a collapse in demand when gas prices fall. For now, CNG has a high price of entry that makes it viable only for taxi services and other fleet operators, but over time, economies of scale may bring down the costs for the ordinary car buyer. And if gasoline stays above $3 a gallon, that change may come sooner rather than later.  Chemistry Class As the name implies, natural gas is a naturally occurring fuel source and also a byproduct of petroleum extraction. In its raw state, natural gas can be extracted either pure or as a heady cocktail of methane, ethane, propane, butane, and pentane, as well as nitrogen, carbon dioxide, water vapor, and other compounds. Refineries strip away virtually everything in the mix, leaving methane as the primary component, with a few other compounds added. Methane is the simplest of carbon-based gases: just one carbon atom and four hydrogen atoms. As a result, it&amp;#039;s also clean burning, with combustion resulting in one carbon-dioxide molecule and four water molecules, lower greenhouse emissions than any other fuel except hydrogen. Under the Hood: CNG Conversion All CNG tanks must withstand the same standards for impact and puncture resistance as an under-car gasoline fuel tank while also vastly exceeding the strength requirements. There are four types of tanks, each lighter and more expensive than the next. Type I is an all-metal tank, generally steel or aluminum. Type II is a thinner metal tank wrapped around the middle with a fiberglass or carbon composite. Type III is a thinner metal tank fully wrapped in composite. Type IV is a plastic tank fully wrapped in carbon-fiber composite--very lightweight, but it comes at a hefty price. What You&amp;#039;ll Need for a Natural Gas Conversion  It doesn&amp;#039;t take much besides a new fuel tank to convert a gasoline-burning engine to one that also runs on natural gas. Attached to the fuel tank [1] is the regulator [2], which reduces tank pressure from 3600 psi to 125 psi. Fuel is then fed to a parallel fuel rail [3] and to new, secondary injectors plugged into an adapter [4]. A wiring harness [5] plugs into the factory engine-control unit and intercepts throttle information, sending it to a new fueling computer [6], which slightly alters the data and passes it to the CNG injectors [7] through a parallel wiring harness [8].  "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/how-to/a7487/should-you-convert-your-car-to-natural-gas/>