Contents:
- Introduction to Natural Gas Vehicles
- Characteristics of Natural Gas for Use in Vehicles
- Reasons for Switching to Natural Gas
- Emissions from Natural Gas Vehicles Compared to Gasoline and Diesel Vehicles
- Performance of CNG Vehicles
- Distribution and Storage of Natural Gas for Vehicles
- Refueling Infrastructure of Natural Gas
- Safety Measures for CNG Vehicles
- Fuel Price and Supply of CNG
- Financial Sustainability of Natural Gas Vehicles
- Health Effects of CNG Vehicles
Introduction to Natural Gas Vehicles:
ADVERTISEMENTS:
In response to emerging epidemiological evidence of the toxicity of gasoline and diesel emissions, there is growing interest in substituting conventional auto fuels with natural gas in cities where ambient air quality is considered unsatisfactory. Natural gas is a clean-burning alternative fuel with a significant potential for reducing harmful emissions from vehicles.
Over 1.5 million vehicles run on natural gas worldwide., Argentina, Italy, Pakistan, Brazil, United States, Canada, New Zealand and Russia are some of the countries operating large number of natural gas vehicles. Argentina and Italy account for more than 50 percent of the global fleet.
The number of natural gas vehicles in India has increased recently after the Supreme Court of India’s decision in 1998 mandating natural gas operation of all the commercial vehicles in Delhi. By mid-2001 there were close to 45,000 natural gas vehicles including about 15,000 buses in Delhi. The current CNG fleet of about 15,000 buses in Delhi, is the largest CNG bus fleet in the world.
While originally CNG was more popular for use in cars, many cities have recently inducted CNG buses for urban operation. Transit buses, traditionally fueled by diesel, are significant emitters of particles, which are known to cause illness and premature deaths. In U.S and Europe natural gas buses are deployed in cities with serious air pollution problems.
Compared with conventional diesel- fueled buses, CNG fueled buses have lower NOx, CO and PM emissions. Combustion of CNG does not emit SO2. Transit buses, three wheeler autos and taxis are high usage vehicles in urban areas that operate in heavily congested city centers where air quality improvements are critical. As such they are good candidates for achieving emission reductions and substituting natural gas for conventional gasoline and diesel fuels is one-way of reducing particles and air-borne toxins dramatically.
World-wide, natural gas vehicle commercialisation activities have taken place for varying reasons in different countries since their initial introduction in Italy in the mid-1930s. Each country has a different set of market conditions, economics, gas availability/supply, technology development etc.; that cause natural gas vehicle commercialisation to progress at different rates.
ADVERTISEMENTS:
Availability of natural gas and existing pipelines and distribution network are responsible for natural gas commercialization activities in Argentina. Availability of natural gas from neighbouring Algeria and the existence of gas pipe lines, distribution network and refueling stations are responsible for natural gas commercialization in Italy. The Italians are product leaders worldwide, exporting vehicle conversion kits, compressors and other natural gas vehicle systems to many countries including India.
The review of natural gas vehicles programme in different countries reveals that natural gas vehicles have been a commercially successful proposition in countries which have adequate indigenous resources of natural gas, a well-developed gas grid and a long established usage of gas as domestic/commercial fuel.
Natural gas vehicles have also been successful in countries (like Italy) which do not have enough indigenous gas production to meet the domestic demand but have access to gas from neighbouring countries, along with a well-knit gas pipe line network set up either for historical reasons, or to meet cold climate requirements for heating and cooking purposes.
Availability of a gas pipeline connecting the city where CNG is to be dispensed is a pre-requisite for its use by the vehicles. Therefore, the feasibility of using CNG in any country as an alternative auto fuel would depend not only on the availability- of natural gas in the country, but the feasibility of laying of natural gas pipelines connecting various cities. Where an elaborate pipe line and pipe line grid does not exist, natural gas economics becomes unfavorable and promoting natural gas vehicles is tough, despite tax concessions and subsidies.
ADVERTISEMENTS:
Natural gas is available in India in substantial quantities in Gujarat, Godavari basin in Andhra Pradesh, Assam and Mumbai. With the installation of HBJ natural gas pipe line, natural gas is available in and around Delhi and Mumbai. With the recent natural gas discoveries in Krishna-Godavari basin, natural gas pipe lines may come up soon for Hyderabad, Chennai and Bangalore. For other cities, it may be difficult to lay natural gas pipelines in the near future.
Characteristics of Natural Gas for Use in Vehicles
:
After coal, natural gas is the world’s most abundant fossil fuel with proven reserves estimated to be twice those of petroleum. Natural gas is extracted from underground from gas wells or oil wells in conjunction with crude oil production. Most of the oil wells produce about 40 percent crude oil and 60 percent natural gas.
Natural gas contains predominantly methane (95 to 99 percent) with the balance made up by other gases (such as ethane and propane). It is used mostly in power generation, industry, fertilizer manufacture, domestic sectors and in the transport sector. Large quantities of natural gas are transmitted and distributed by land through gas pipe lines.
ADVERTISEMENTS:
For bulk shipment by sea or train, it is liquefied and maintained at cryogenic temperatures as liquid natural gas (LNG). It is also transmitted in compressed form in cylinders for short distances. For use as an auto fuel, it is stored in vehicles in heavy cylinders as a gas pressurised to about 3,000 pounds per square inch (or about 200 bar) and at ambient temperatures as CNG.
The octane number of natural gas is more than 120. In terms of energy content, one kg of natural gas is equivalent to about 1.3 litres of gasoline and 1.2 litres of diesel. On a volume basis, one cubic meter of CNG (at about 200 bar) is equivalent to about 1.10 litres of gasoline and 1.00 litre of diesel.
Reasons for Switching to Natural Gas
:
There are two principle reasons for switching to natural gas. One is the significantly lower exhaust emissions, especially particulate matter. This is the primary reason for the promotion of natural gas buses in the United States, as well as the Supreme Court of India’s decision in Delhi, India. The second reason is the diversification of energy resources. This has been the historical reason for switching to natural gas in some of the countries like Argentina.
Worldwide, natural gas reserves are more abundant than oil reserves, giving greater potential to the use of natural gas. A country that imports oil but has an abundant supply of natural gas may find it particularly attractive to consider natural gas as a transport fuel in order to reduce its oil import bills.
Bangladesh and Indonesia (where crude oil production will cease in less than a decade at the current rate but abundant supplies of natural gas remain) cite this as the reason for wanting to promote natural gas vehicles.
There are cases of oil importing countries with indigenous natural gas reserves where switching to natural gas is not necessarily financially favorable. Pakistan illustrates this point. In Pakistan, as in India and in many other South Asian countries, diesel has historically been priced at one-half that of gasoline. As a result, it is not uncommon to see cars and light duty gasoline vehicles convert to diesel.
Partly as a result of this pricing policy, the consumption of gasoline is less than a fifth of that of diesel. While Pakistan imports bulk of its diesel, it has become a net exporter of gasoline and naphtha (which is used in gasoline production).
Because of Pakistan’s inter fuel pricing policy, natural gas has displaced only gasoline and not diesel-it is much more attractive for vehicle owners to switch from gasoline to natural gas than from diesel to natural gas-worsening the supply demand imbalances and forcing the refineries to export even more naphtha and gasoline at a loss.
Emissions from Natural Gas Vehicles Compared to Gasoline and Diesel Vehicles
:
Given equal energy efficiency, emissions from natural gas vehicles will be lower than gasoline and diesel vehicles, since natural gas has lower carbon content per unit of energy. In addition, the high octane value of natural gas (Research octane number of 120 or more) makes it possible to attain better combustion and thermal efficiency by increasing compression ratio.
Natural gas vehicles have lower exhaust emissions of non-methane hydrocarbons, particulate matter, CO and CO2. Compressed natural gas vehicles produce about one-tenth of non-methane HC emissions compared to their counterpart gasoline engines. With CNG, formaldehyde emissions are reduced by 50 percent and acetaldehyde emissions are reduced by 80 percent compared to their counterpart gasoline vehicles. Benzene and 1-3 butadiene are virtually nonexistent in CNG exhaust.
Dedicated natural gas vehicles can enjoy a considerable exhaust emissions advantage over conventional diesel engine vehicles. In particular, visible smoke is virtually eliminated.
A comparison of emission test results of comparable conventional diesel and CNG buses is shown in Table 7.1 below:
The reduction in emissions in going from conventional diesel to dedicated CNG buses is dramatic.
The emission results from a Euro-2 diesel bus and CNG bus manufactured by an Indian vehicle manufacturer as presented in Mashelkar Committee report is indicated in table 7.2.
It can be seen that CNG has a clear advantage in terms of particulates and oxides of nitrogen but the carbon monoxide and hydrocarbon emissions are higher. The comparison is between a diesel vehicle without catalytic converter with a CNG vehicle fitted with a catalytic converter and hence deterioration of catalytic converter over a period of time may result into much higher CO and HC emissions.
A recent study by Harvard university (August 2001) concludes that “CNG vehicles for mile emits 20 percent more greenhouse gases than driving a comparable diesel vehicle for one mile. From the perspective of global warming, the decision to switch from diesel to CNG is a harmful one. CNG vehicle emits 80 percent less particulate matter, 25 percent less nitrous oxides, the output of carbon monoxide and carbon dioxide are significantly greater than for diesel”.
Performance of CNG Vehicles
:
Studies indicate that the performance of CNG vehicles introduced before 1990 and in the early 1990s was less than satisfactory. They suffered from maintenance, fuel economy and reliability problems compared to conventional fueled vehicles.
The fuel economy of natural gas buses is lower than that of diesel buses on an energy equivalent basis by about 20-35 percent. IVECO, one of the large manufacturer’s of diesel and CNG buses estimated that CNG buses which weigh some 700 kgs more than its Euro3 equivalent diesel counterpart, consumes 25 percent more energy.
Natural gas buses tend to be less reliable than their diesel equivalents even in the best of circumstances. Recent studies by International Association of Natural Gas Vehicles indicates that in some cases, reliability of natural gas vehicle buses is only half that of diesel equivalents. In CNG buses, many difficulties were experienced with spark plugs, coils and ignition leads both in terms of life and other difficulties.
CNG fuel pressure regulation and engine over heating were reported as common problems in U.S. CNG buses. Back firing was often reported as a concern in many U.S. buses, although this problem has been reduced to much more tolerable levels in the latest vehicles. In Jakarta, Indonesia, a recent World Bank study reported that of the 40 dedicated CNG buses, only 20 are operating owing to maintenance problems.
A diesel engine converted to a CNG engine has different speed-torque characteristics, which leads to the problems of clutch plate failures, overheating, loss of power etc.
In November 2001, Delhi Transport Corporation reviewed the performance of over 1500 CNG bus fleet with its diesel fleet and summarized as below:
3.32kms/kg with CNG against 4.46kms/kg (3.75kms/litre) with diesel.
Power loss, gas leakage, starting trouble, engine overheating, cylinder head failure, spark plug problems and frequent breakage of silencer muffler etc., were noticed in CNG buses.
According to Rakesh Mehta, the then chairman of Delhi Transport Corporation, “there are problems of sturdiness of technology, cost of spare parts, safety and regulation which still needs to be addressed. It may take some years before the CNG engine technology stabilizes in Delhi. Studies indicate that continual operational problems with natural gas buses are certain to invite a back lash from bus operators seriously harming the future of natural gas vehicle industry”.
Distribution and Storage of Natural Gas for Vehicles
:
Large quantities of natural gas are transmitted and distributed by land through gas pipe lines. The volume of gas consumed in the transport sector is not sufficient to justify the construction of natural gas pipelines even in large cities. Without the existence of a network of pipelines for other users of natural gas (industrial, commercial and domestic), a viable natural gas vehicles program would not be possible.
In the year 2000, CNG and LNG vehicles consumed 385 million cubic metres of natural gas in total in the United States. In comparison, a 500 megawatt power plant operating 5000 hours a year (57 percent utilization) at 50 percent efficiency consumes about 500 million cubic metres of gas. That is to say, one 500 megawatt power plant consumes more natural gas than all natural gas vehicles in the United States put together.
In India, having regard to the country’s vastness, natural gas vehicles can be commercially viable only in the cities where natural gas pipelines exist or would be laid in future. Cost of establishing fresh grids are quite high and for that reason alone it may not be feasible to dispense CNG for automotive purposes in most Indian cities in the near future.
Refueling Infrastructure of Natural Gas
:
During refueling, natural gas has to be compressed to a pressure of about 3000 pounds per square inch (about 200 bar) typically requiring about 0.2-0.3 kilo watt hours (kwh) of energy per cubic metre of gas. Refueling technology is one of the key elements in developing a successful market for natural gas vehicles which, on average require refueling twice as frequently as gasoline vehicles.
There are two types of natural gas refueling systems- fast fill and slow fill. A slow fill cost less to set up but takes half an hour or more to fill a tank. A fast-fill takes only a few minutes. In the United States, typical cost for setting up a slow fill station is of the order of U.S $ 0.35 million and a fast fill station US $ 2.7 million. A fast fill station in India costs between Rs 1-2 crores. CNG infrastructure costs are 5 to 8 times that for diesel. The high cost of refueling equipment gets reflected in the increasing cost of CNG and in CNG vehicle operating costs.
The high pressure cylinders needed for CNG in vehicles weigh more and occupy more space. Depending on its material, construction, a CNG cylinder weighs five times as much as a gasoline tank to provide the same amount of energy Space and weight considerations in cars, two and three wheelers and multi utility vehicles restricts the maximum number of CNG cylinders in the trunk to two or three. This limits the travel range of vehicles before refueling.
In addition, CNG is less readily available than gasoline or diesel at retail fuel stations in many urban centres and may not be available at all in rural areas outside urban centers. For these reasons, gasoline or diesel fuel cars are not converted to CNG by private vehicle owners. However taxi and 3 wheeler vehicle operators who operate within the city limits prefer to convert their vehicles to CNG in areas (like in Pakistan and Delhi) where there is significant difference between gasoline and CNG prices.
CNG fueled urban buses have no problems of space for cylinders since they are kept either in the chassis area or on the roof of the buses and hence may not be affected by the range. However the cost of cylinders adds to the initial capital cost of the vehicle. A further concern about the additional weight of CNG cylinders is associated with reduction in acceleration, need for longer braking distances and decrease in fuel economy.
When launching a natural gas vehicle programme, one logistical problem is the balance between the number of natural gas vehicles and refueling stations. Any imbalance-either in the form of oversupply of refueling stations or a disproportionately greater number of vehicles relative to refueling capacity-would result in either very low returns for refueling station owners, or long queues for vehicle drivers tarnishing the industry’s public image-similar to what happened in Delhi during 2002.
Inadequate refueling infrastructure (shortage of refueling stations), was partly responsible for conversion back to gasoline from CNG in Bangladesh in the 1990s. Long queues at CNG refueling stations in Delhi are a significant source of dissatisfaction among drivers today. During 2001-2002, the CNG queues in Delhi became longer and bus operators including Delhi Transport Corporation could get gas only after waiting for 8 to 10 hours.
Safety
Measures for CNG Vehicles:
Refueling of gasoline and diesel in vehicles is a relatively simpler operation requiring transfer of fuel at ambient conditions whereas CNG is fueled at a very high pressure of 200 bar (i.e. 200 times the atmospheric pressure). Refueling is one of the least safe moments in the use of natural gas as a transport fuel.
In a recent example from Delhi, a car converted to run on compressed natural gas exploded during refueling as the gas cylinder failed, injuring five people. The cause was identified to be the poor quality of the gas cylinder. Any leak from the filling nozzle or CNG kit and its connecting pipe needs to be stopped immediately which otherwise may lead to an accident/fire/explosion.
Therefore, it is essential that filling operator is well aware of the laid down safety precautions including basic checks on the CNG cylinder and the associated kit. The filling station operators are required to be trained and certified fit for the job.
Because natural gas is lighter than air, it will not lie along the ground if it leaks, and is thus safer in an accident. One of the major concerns with the use of natural gas in vehicles is the possibility that excess vapour pressure might be vented from inactive vehicles left in an enclosed area such as a garage for long periods of time, possibly causing an explosion.
Parking CNG vehicles in an enclosed building can become a problem if any system leakage is present. Appropriate roof venting is necessary to ensure that natural gas exits the building. Garages for natural gas vehicles must be designed with good ventilation at the ceiling level.
CNG storage cylinders are to be built to rigorous quality standards. The use of composite materials can reduce the weight of the cylinders and increases safety considerably. Internationally acceptable standards for gas cylinders, refueling stations, gas dispensing units, conversion kits, natural gas vehicle engines, garages and the quality of gas should be set.
Adequate monitoring and inspection systems to enforce these standards are essential to improve safety. Use of non-standard CNG kits and cylinders may result in their catastrophic failure. In Delhi, during 2002, a total of 12 CNG vehicles are reported to have caught fire, or have had explosion due to this reason.
Fuel Price and Supply
of CNG:
Owing to transportation difficulties, the cost of natural gas varies greatly from country to country and even within countries. Where gas is available by pipeline from the field, its price is normally set by competition with residual fuel oil or coal as a burner fuel. The market clearing price of natural gas is typically around U.S $ 3 to $ 4 per million BTUS. Compression costs can add another U.S $ 2 per million BTUS.
CNG’s potential as a vehicle fuel is strongly affected by its price in the local market. Although natural gas is much cheaper to produce than gasoline or diesel, it is much more expensive to distribute and compress before refueling.
The details of the costs of gasoline, LPG and CNG at the current level of duties and taxes in Delhi as worked out by Mashelkar Committee is shown in Table 7.3 below:
In Delhi, while the price of gasoline is Rs 17.70 per kg, the price of CNG is Rs 18.70. However while the customs and excise duty on gasoline is Rs 16.80 per kg for gasoline, it is only 3.00 per kg for CNG. The sales tax imposed by the State government is Rs 6.70 per kg of gasoline and it is nil for the CNG. Though the basic price of gasoline is one rupee per kg less than CNG, its end price (Rs 41.20 per kg) is almost double that of CNG (Rs 21.70 per kg).
Though at the current level of duties and taxes, CNG would be competitive with gasoline and diesel, the Central and State governments are foregoing excise and sales tax revenues on the sale of gasoline and diesel to the extent they are substituted by CNG. To make the use of CNG competitive and sustainable, support of the Central and State governments by way of lower taxes and duties would be necessary.
The cost of dispensing CNG in Delhi is lower than gasoline and LPG, because a gas transportation pipeline to Delhi is already available, and the natural gas is being priced below the fuel oil parity price. Calculations show that when natural gas is priced at fuel oil parity price, CNG may become costlier than LPG. In most countries, where CNG is used as an alternative auto fuel, city gas pipeline network for supplying gas for domestic consumption for heating and cooking purposes exists.
According to Mashelkar Committee, “Calculations further show that in the Indian context, laying of a gas pipe line for supplying natural gas to the cities away from a gas supply source may not be an economically feasible proposition, unless that city requires natural gas for bulk industrial consumers like power and fertilizer plants as well. Thus CNG, as an alternative auto fuel, is expected to remain limited to the cities which have an existing gas pipelines. In such cities also, the cost of supplying CNG will be higher than the conventional auto fuels, gasoline and diesel”.
To ensure that the switch over is sustainable, substitution of liquid auto fuels by gaseous fuels would need government support by way of lower taxation on gaseous fuels. Revenues of Central and State Government’s from petroleum products being substantial, the fiscal support which the governments, particularly the State governments could provide would depend on their ways and means position.
Financial Sustainability of Natural Gas Vehicles
:
Natural gas vehicles have a higher initial capital cost and higher operating cost than a diesel vehicle. In India, a CNG bus costs Rs. 16 lakhs compared to Rs 9 lakhs of a diesel bus. Natural gas buses are about 30 to 40 percent more expensive to maintain and are less reliable compared to diesel buses. The fuel economy of natural gas buses is lower than diesel buses on an energy equivalent basis, by atleast 10 to 15 percent and typically even more.
The Delhi experience indicates that natural gas vehicles currently costs 30 % more to purchase are less fuel efficient and costs 30% more to operate than conventional diesel fueled vehicles. They are less reliable and are not cheaper than conventional diesel fueled vehicles over their life cycle in Delhi, India. Refueling, maintenance and bus storage infrastructure is also expensive. The international experience is the same and many have decided to stay with natural gas despite the economic discentives purely on environmental grounds.
In U.S, Federal Transit Administration subsidises upto 83 percent of the capital cost of new natural gas buses. Air quality funds off set most of the different capital and some of the infrastructure costs. The Federal government supports natural gas vehicles by imposing lower taxes on CNG- 1.5 cents per litre on CNG against 6.3 cents per litre on diesel. The federal government gives grants upto U.S. $50,000 per bus and upto U.S $1,00,000 per refueling station and allows tax deductions for natural gas vehicle operators.
In Delhi and other cities in India, it is difficult to introduce and maintain natural gas vehicles without large subsidies and financial incentives from the government. The city transport undertakings in India even with diesel bus operation are incurring huge losses and are cash-strapped. Hence the penetration and long term sustainability of natural gas vehicles in Indian cities depends on government policies, subsidies and financial incentives.
The temptation to mandate natural gas buses in man; other Indian cities is strong for various reasons. But mandating what would otherwise be commercially unsustainable in the long run cannot be a viable solution. Hence if some of the State governments are serious about promoting natural gas buses, they must first examine the viability of natural gas distribution system in the city and also the broader issues facing public transport.
Issues concerning fare structure and how to create level playing ground for natural gas bus operators compared to informal sector operators like three wheeler autos and two wheelers are very important.
Because CNG vehicles are more expensive to purchase than vehicles powered by liquid fuels, for the NGV programme to be financially sustainable in the long run, the incremental cost must be recovered in the form of lower operating and maintenance costs. The lower cost in turn typically has to come from fuel costs. The viability of natural gas vehicle programme therefore rests on CNG fuel price compared to other auto fuels.
Studies in Delhi have indicated that replacing diesel buses with high cost CNG buses may result in unforeseen negative consequences both in social effects and mobility practices. Studies in Delhi suggest that replacement of diesel buses by CNG buses will result in increased bus fares which will result in about 10-15 percent of bus users shifting to two wheelers or cars. This shift would increase congestion, pollution and accidents.
The basic principle of promoting public transport is to keep fares below marginal cost of using the cheapest form of private mechanised transport. The studies indicate that CNG buses would result in the bus fares in the range of Rs 700-1000 for chartered buses used by commuters (against Rs 450 by the current diesel buses) and against an expenditure of Rs 450 per month by two wheelers.
Health Effects of CNG Vehicles:
The health effects of CNG and diesel emissions in general and particulate matter emissions in particular were studied by many institutions. The recent studies made by West Virginia State University and Harvard Centre for Risk Analysis is considered important. The recent West Virginia university study concluded that “CNG and LNG fueled engines have significantly reduced total mass emission rates of particulates, but a larger portion of this total is “ultra-fine” particulates.”
The study conducted on 60 buses in Dallas city concluded that “On a mass basis, CNG buses emitted less particulate matter, but on a count of the particles, the CNG buses were equal or higher than diesel buses”. The recent Harvard Centre for Risk Analysis study concluded that, “while CNG reduces emissions of particulates, it may generate more “ultra-fine” particles (less than 0.01 micron) than diesel”.
The recent studies indicate that the potential of a particle to penetrate tissue barriers easily and reach the deeper respiratory system is more with fine particles than larger particles. The controversy on health effects of diesel vs CNG vehicles continues.
The health effects of CNG vehicles need further study. On 28 August 2001, the Times of India in an article on vehicle pollution concluded that “the public perception on pollution is largely based on visible forms but the relationship between visibility- and pollution is complex and there is a need for greater scientific investigation”.