Compressed natural gas



Compressed Natural Gas (CNG) is a substitute for gasoline (petrol) or diesel fuel. It is considered to be an environmentally "clean" alternative to those fuels. It is made by compressing natural gas (which is mainly composed by methane (CH4), in a percantage range of 70% to 98%). It is stored and distributed in hard containers, at a normal pressure of 200/220 bar, usually in cylindric of spherical shapes to maintain equal pressure on the walls of the containers.

In response to high fuel prices and environmental concerns, compressed natural gas is starting to be used in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, and in transit and school buses.

Technology
CNG can be used in Otto-cycle (gasoline) and modified Diesel cycle engines. Lean-burn Otto-cycle engines can achieve higher thermal efficiencies when compared with stoichiometric Otto-cycle engines at the expense of higher NOx and hydrocarbon emissions. Electronically-controlled stoichiometric engines offer the lowest emissions across the board and the highest possible power output, especially when combined with EGR, turbocharging and intercooling, and three way catalytic converters, but suffer in terms of heat rejection and fuel consumption. A suitably designed natural gas engine may have a higher output compared with a petrol engine because the octane number of natural gas is higher than that of petrol.

CNG may be refuelled from low-pressure ("slow-fill") or high-pressure ("fast-fill") systems. The difference lies in the cost of the station vs. the refuelling time. There are also some implementations to refuel out of a residential gas line during the night, but this is forbidden in some countries.

CNG cylinders can be made of steel, aluminium, or plastic. Lightweight composite (fibre-wrapped plastic) cylinders are especially beneficial for vehicular use because they offer significant weight reductions when compared with earlier generation steel and aluminium cylinders, which leads to lower fuel consumption.

The equipment required for CNG to be delivered to an Otto-cycle engine includes a pressure regulator (a device that converts the natural gas from storage pressure to metering pressure) and a gas mixer or gas injectors (fuel metering devices). Earlier-generation CNG conversion kits featured venturi-type gas mixers that metered fuel using the Venturi effect. Often assisting the gas mixer was a metering valve actuated by a stepper motor relying on feedback from an exhaust gas oxygen sensor. Newer CNG conversion kits feature electronic multi-point gas injection, similar to petrol injection systems found in most of today's cars.

Drawbacks
Compressed natural gas vehicles require a greater amount of space for fuel storage than convention gasoline power vehicles. Even though it is a compressed gas, rather than a liquid like gasoline, CNG takes up more space for each GGE (Gallon of Gas Equivalent). This makes it difficult to design smaller vehicles that look and operate like the vehicles that people are accustomed to.

Furthermore, using CNG does not escape paying higher fuel prices, as CNG price increases are a derivative of gasoline price increases, still nowadays is absolutely more convenient than traditional fuels, as its price is in a range of 1/3 to 1/2 compared to benzine, in Europe.

CNG compared to LNG
CNG is often confused with liquefied natural gas (LNG). While both are stored forms of natural gas, the key difference is that CNG is in compressed form, while LNG is in liquefied form. CNG has a lower cost of production and storage compared to LNG as it does not require an expensive cooling process and cryogenic tanks. CNG requires a much larger volume to store the same mass of natural gas and the use of very high pressures (3000 to 4000 lbf/in², or 205 to 275 bar).

Europe
In Germany, CNG-generated vehicles are expected to increase to two million units of motor-transport by the year 2020. The cost for CNG fuel is between 1/3 and 1/2 compared to other fossile fuels in Europe. Citation needed

South America
Argentina and Brazil, in the Southern Cone of Latin America, are the two countries with the largest fleets of CNG vehicles. Conversion has been facilitated by a substantial price differential with liquid fuels, locally-produced conversion equipment and a growing CNG-delivery infrastructure. A 'Blue-network' of CNG stations is being developed on the major highways of the Southern Cone (including Chile and Bolivia) to allow for long-haul transportation fuelled by CNG.

Asia
In Asian Developing Economies such as India, CNG costs are at Rupees 19.20(USD $ 0.50 Cents) per Kg compared with Rs.43.9 (US$ 1.5) per Liter of Petrol.

The Cost saving is immense along with reduced Emissions and Enviorment friendly cars.



Significantly CNG has been made mandatory for all Public Transport in the Capital City of New Delhi.

CNG has grown into one of the major fuel sources used in car engines in Pakistan, Bangladesh and India. The use of CNG is mandated for the public transport system of India's capital New Delhi as well as for the city of Ahmedabad in the state of Gujarat. The Delhi Transport Corporation operates the world's largest fleet of CNG buses. The government of Punjab, Pakistan, the most populous province of that country, has mandated that all public-transport vehicles will use CNG by 2007. Today many rickshaws as well as personal vehicles in India and Bangladesh are being converted to CNG powered technology, the cost of which is in the range of $800-$1000. In the Bangladesh capital of Dhaka not a single auto rickshaw without CNG has been permitted since 2003. As of July 2007 Pakistan is the largest user of CNG in Asia, and second largest user in the world (http://www.iangv.org/ngv-statistics.html).

According to the International Association for Natural Gas Vehicles, Pakistan has the second-largest number of natural gas vehicles. In the Middle East and Africa, Egypt is a top ten country in the world with more than 63000 CNG vehicles and 95 fuelling stations nationwide. Egypt was also the first nation in Africa and the Middle East to open a public CNG fuelling station in January 1996.

Oceania
During the 1970s and 1980s, CNG was commonly used in New Zealand in the wake of the oil crises, but fell into decline after petrol prices receded. Brisbane Transport and Transperth in Australia have both adopted a policy of only purchasing CNG buses in future. Transperth is purchasing 451 Mercedes-Benz OC500LE buses, including 58 articulated buses, while Brisbane Transport has purchased 216 Scania L94UB and 180 MAN 18.310 models as well as ordering up to 30 articulated CNG buses on MAN chassis'.

In the 1990s Benders Buslines of Geelong, Victoria trialled CNG buses for the Energy Research and Development Corporation.