ALTERNATIVE FUEL

Compressed Natural Gas

Introduction:

The demand for petroleum products has been increasing at a rate than increase in a domestic availability, resulting in increased imports. The transport sector is the single largest consumer of petroleum products. In wake of this there is urgent need to introduce alternate fuels as substitute for high-speed diesel and petrol in the transport sector.

Transport sector contributes to the growth of economy and performs to exercise greater economy over existing source of energy and more logical integrated usage patterns of existing resources.

Efforts in form of research and around the world in the automotive fields is altered towards to develop the engine running on alternative fuels which could be replenished and contribute to very low air pollution. The continuing pressure on emissions control through periodically tightened regulations has compelled the search for the alternate fuels as also alternate power plants. Among the available options to petrol and diesel the CNG has received a great deal of attention and has already been applied successfully to over a million vehicles in the various parts of the world such as Argentina, Russia, Italy and gaining the increasing acceptance particularly in taxies, buses, delivery trucks, and garbage tippers.

What is CNG

Natural gas is available in large quantities in India and does not elaborate processing or refining, as it is required in the other petroleum products. CNG consists of mainly methane with low percentage of other hydrocarbons like ethane, propane. It has low levels of pollution does not materially restrict vehicle performance, and is far more economical to use than petrol.

The composition of CNG can vary from place to place and manufacture-to-manufacture but ideal composition is shown in table below

TABLE NO.1

Constituent	Percentage	Limit
Methane	90%	Minimum
Ethane	4%	Maximum
Propane	1.7%	Maximum
C4	0.7%	Maximum
Co2+n2	0.2%	Maximum
Hydrogen	0.1%	Maximum
Carbon monoxide	0.1%	Maximum
Oxygen	0.5%	Maximum

Natural produces less air pollution than any other fossil fuel use of CNG vehicles can reduce carbon monoxide emissions as much as 93%,nitrogen oxide reduces about 33% and hydrocarbons are reduced by about 50% natural gas emits almost no carcinogenic particulate.

By using CNG power vehicles, a by fuel tank can exist; therefore in locations without CNG pumps gasoline may be used by just switch. Since CNG is a clean burning fuel, maintenance costs are lowered. CNG has octane no.130, which is considerably higher than 95 octane no. for gasoline. Consequently, the CNG vehicle is more energy efficient.

Besides using natural gas to power vehicles it is also used for power generation.

Increased power and thermal efficiency

CNG has a higher octane no. Than the petrol and it is possible for CNG engines to operate at a higher compression ratio than petrol engines without knocking. The fuel efficiency of CNG is therefore better than that of the petrol engines.

Typical emission reduction in a CNG bus as compared to diesel bus.

TABLE NO.2

Effluent	Percentage reduction
Carbon monoxide	56%
Hydrocarbons	55%
Nitrogen oxide	56%
Particulates	86%

CNG represent a more cost effective reduction measure than a quite a few options available for diesel engines.

Properties of CNG

The properties of CNG are almost similar to methane. Methane has a very good antiknock qualities means it does not ignite readily. Antiknock ratio as high as 12:1 compared with petrol engines maximum 10:1. the CNG fuel used engines have higher thermal efficiency as compared to the fuelled by gasoline.

In addition this there is reduction in the pollutants emitted by CNG is noticeable. CNG is nontoxic and lighter than air so when leakage occur it quickly disappears unlike gasoline, which evaporates. Ethane and propane, which are present in very small amount, can affect the burning properties of CNG.

Both the gases try to lower the octane characteristics and causes pre ignition and reduced fuel efficiency.

TABLE NO.3

Properties	Unleaded Gasoline	Diesel	CNG
Boiling range ⁰ c	27-215	160-380	-160
Density(gm/cc)	0.69-0.7851	0.785-0.881	0.13
Energy(kg/kcal)	44700-49800	43800	52000
Ignition temp	230-480	200-260	730
Octane number	87-93	N/A	120
Flash point	-43	52	-183
Flammability	1.4-7.6	.007-.5	5.3-1.4
Flame speed	0.4	0.4	0.34

Advantages of CNG

1. It’s cheap:

CNG currently costs about 25to50% less than gasoline additionally it need not require refining and creates no harmful by products that require expensive handling.

2. It’s engine friendly:

Natural has an octane no. 130 compared with 95 of the unleaded gasoline because of the combustion efficiency of natural gas, NGV’s have better maintenance costs and longer engine life as compared to other liquid fuels.

3. It’s safe:

Natural gas is lighter than air so if leakages occur it safely dissipates to atmosphere. Natural gas safe to transport because natural gas pipe lines are located under ground.

4.There is lots of it:

Experts agree that there is enough natural gas to last well beyond 21st century .natural gas is the 2^nd most abundant fuel available in India after coal.

5. It’s made in India:Most of production of gas comes from western offshore area,Andhra Pradesh and GUJRAT being major producer of natural gas while Tripura, Tamilnadu and Rajasthan being the minor one.

6.It is easy to tap:

Transportation of natural gas is very easy it can laid on pipes and can be transported to cities .Natural gas for vehicles can be provided at virtually at a any point along the pipeline network.

7.It’s clean: Natural gas is gaseous in nature it mixes with air completely and combustion is proper, that is why natural gas vehicles produce low level of pollutants.

8.It’s odorless

Disadvantages of CNG:

1. Storage cylinder takes lot of space as the gas once filled has to travel almost 400 kilometers but now a day’s by fuel and dual fuel engines which run on CNG and other fuel.

2. Loss of power.

3. CNG stations are not widely spread in India.

4. Expensive engine modifications.

Liquefied Natural Gas (LNG)

To liquefy the natural gas, cryogenic technology is used. Cryogenic technology is the branch of physics, which deals with behavior of materials at low temperature. Because of use of this technology, the high powered refrigeration and compression consumes as much as 25% of energy of natural gas. This downsizes some of cost, benefits of natural gas.

LNG is a positive option for heavy-duty trucks. It covers long distances without time consuming refueling it burns clean and is very economical.

LNG has to kept cold to stay liquefied, therefore it is stored in the stainless steel inner tank with steel or ALUMINIUM outer tank .The space between tanks is filled with an extremely efficient insulating material (i.e aluminized Mylar and silk setting ) all air is removed from space.

Advantages of LNG:

1.Abundant supplies.

2.Low emission vehicle.

3.Inexpensive

4.Reduced engine maintenance.

Disadvantages:

1.New refueling site is required.

2.Expensive engine modification .

3.Cryogenic technology is necessary.

Economy of CNG

CNG is the most economical fuel and saves more than 55% of our fuel expenditure over petrol.

The lubricating oil life is considerably extended too because CNG does not contaminate and dilute the crank case oil.

It eliminates frequent vehicle maintenance.

Due to absence of any lead content in CNG, the lead fouling of plugs is eliminated and plug life is greatly extended.

	Petrol	CNG
Cost per liter	RS. 36.00	RS. 15.00
Cost of 8 litres	RS. 288.00	RS.120.00
Monthly consumption	RS. 8640.00	RS. 3600.00
Yearly consumption	RS. 103680.00	RS. 43200.00

Clean Alternative Fuels

Compressed Natural Gas One in a series of fact sheets United States Environmental Protection Agency Transportation and Air Quality Transportation and Regional Programs Division. CLEAN ALERNATIVE FUELS CLEANER AIR

In 1999, the U.S. Department of Energy (DOE) con-ducted a study that provided direct, side-by-side cost and emissions comparisons of CNG and gasoline-fueled taxicab operations. The report, Alternative Fuels Case

Study: Barwood Cab Fleet

Study Summary, compared 10 CNG-fueled cars from 1996 with 10 gasoline-fueled cars of the same make and model to determine operating costs.

The study found that the fuel economy of the CNG and gasoline cabs were identical-cal and that operating costs for CNG cabs were 25 percent less than the gasoline-powered cabs. Average fuel costs for the CNG cabs were 32 percent less, and reportedly cost about 15 percent less to maintain than the gasoline vehicles. Tailpipe emissions tests on 14 of the 20 vehicles indicated

that CNG exhaust emissions were significantly lower than their gasoline counterparts for non-methane hydrocarbons and carbon monoxide.

Natural gas is one of the most widely used forms of energy today. It is commonly used to heat and cool homes and businesses nationwide. In addition, more than 85,000 compressed natural gas (CNG) vehicles, including one out of every five-transit buses, are operating successfully today. CNG’s popularity stems, in part, from its clean-burning properties.

In many cases, CNG vehicles generate fewer exhaust and greenhouse gas emissions than their gasoline- or diesel-powered counterparts. CNG is odorless, colorless, and tasteless.

It consists mostly of methane and is drawn from gas wells or in conjunction with crude oil production. CNG vehicles store natural gas in high-pressure fuel cylinders at 3,000 to 3,600 pounds per square inch. An odorant is normally added to CNG for safety reasons.

Two types of CNG fuel systems are on the market: dedicated vehicles, which operate exclusively on natural gas, and dual-fuel vehicles, which can use both natural gas and gasoline. Auto manufacturers offer a variety of both dedicated and dual-fuel CNG vehicles, including compacts, trucks, vans, and buses. The United States has vast natural gas reserves distributed across the country through extensive pipeline systems extending from the wellhead to the end-user. As a result, CNG is currently available at approximately 1,300 refueling stations in 46 states, and this number continues to grow. In addition, CNG vehicle owners can refuel their cars at home by installing small compressors connected directly to the home’s natural gas supply. Actual emissions will vary with engine design; these numbers reflect the potential reductions offered by compressed natural gas, relative to conventional gasoline.

• Fewer toxic and carcinogenic pollutants, and little to no particulate matter produced.

• No evaporative emissions in dedicated engines (such as those associated

with gasoline or diesel).

Estimates based on CNG’S inherently “cleaner” chemical properties with an engine that takes full advantage of these properties.

CNG kits and engine conversion

Conversion of the gasoline engine can be done in following

NG can be used to substitute gasoline of engine which retains the flexibility to switch over to gasoline of NG.

NG can partly substitute diesel in dual fuel engine which can run either diesel or on diesel NG mixture.

Dedicated engine operating on CNG.

Requirements for conversion:

All the vehicles can be converted into operated CNG but the space availability restricts its use in two wheelers. The three and four wheeler can be converted the requirements being for dual mode operation

For any type of vehicle (i.e petrol and diesel):

1.CNG cylinder.

2.Metallic piping for gas .

3.Gas regulator.

For petrol engine additional requirements are:

1.Carburettor injector.

2.Dual curve engine system.

3.Fuel switching devices.

For diesel addition requirements:

1.Gas air mixture.

2.Diesel oil delivery limiting device.

CNG is supplied to consumer mainly through existing CNG stations .The dispensing units at the stations are supplied through storage cascade mother stations in rack mounted cascades to the retail outlets called Daughter stations. The on board cylinder in CNG driven vehicle is refueled from the dispensing unit under pressure in manner similar to petrol filling.

The vehicle cylinder is not taken out or replaced for refueling CNG dispensing operates on the principle of equalizing pressure between the storage cascade and vehicle on board cylinder. CNG is sold on retail from the dispenser in kg units using direct mass flow meters while refueling.

There is reduction in storage pressure with each successive filling at a CNG retail outlet not connects to a gas pipeline. Once station pressure drops the refueling time increases, while the quantity of CNG dispensed to the vehicle decreases. Normally a car with one on board cylinder is refueled in 3 minutes when cascade storage pressure is full.

CNG cylinder

Since the density of CNG is low so gas has to be compressed and stored in heavy steel cylinders that serves as fuel tank .Gas is generally filled upto 160-200bars pressure ,so overall weight is substantial; even after compression to such a high pressure a typical CNG system cylinder with water capacity of 50 liters can hold only 12.5m3 of gas , equivalent to 15.6 liters of gasoline the weight may be up to 45 kilograms thus for every liter of gasoline equivalent of CNG an extra weight of 2kg is required to be carried. Alloy steels are used for storage cylinders of CNG the chrome mo alloy steel is cheapest but heaviest. If composite material is used there is a reduction in weight but increase in costs.

The CNG cylinders life is tested by repeatedly filling and emptying .the work pressure of cylinder is normally 200 bar, testing pressure is 300 bar, while bursting pressure is 600 bar .

Fuelling stations

It is important to establish sufficient no. of fuelling stations for implementation of CNG program in transport sector.

The fuelling stations can be classified in different groups based on two criteria

A. The time taken to refuel a vehicle.

1.Fast fuelling stations

2.slow fuelling stations

3.stations which provide both facilities i.e. combined fast and slow fuelling stations.

B. The ways in which the stations obtain CNG.

1.Compression stations.

2.Transfer stations.

Faster fuelling station:

The refueling time is about 4-10 min for vehicle. For this three or four stage compressor is required for large capacity .Gas storage facilities needed are more to meet peak demand .A high pressure of about 260 bars is attained by roadside retail outlet where vehicles are to be filled fast .The cost of establishment is high, cost is 2-3 times than slow fuelling station.

Slow fuelling station:

The refueling time is 5-8 hours. The compressor needs to attain a pressure of 170 bar since refueling time is long so storage requirement is less so a single or double compressor is ideal for refueling fuel of vehicles with an idle time of 8 hrs.

Application of CNG

CNG substitute different petroleum products in many sector of the economy and also substitute coal in power plants.

The scope for substitution of natural gas for different petroleum products.

Sector	Energy production substitute	NG substitute
Industry	Fuel oil	NG
Fertilizer	Naphtha, Fuel oil	NG
Household pipe	Kerosene	LPG/NG
Transport line	Diesel, petrol	CNG /LNG

The effect of air/fuel ratio on the emission parameter for both engines are shown below, it is obvious that all objectionable emissions for CNG engines are less compared to conventional petrol engines.

FUTURE PLAN

The government is thinking of bringing legislation in parliament to make it compulsory for all buses to run on CNG, to check the vehicle pollution level in country.

At the industry level bajaj auto, country’s largest three wheeler manufacture seeks to exploit the technology to combat pollution.

Mechanical Engineering seminars

Saturday 24 August 2013