Pollution from Motor Vehicles – Urgency of development of environment-friendly, cleaner system for road transport:
A. Introduction: Pollution from motor vehicle is the single largest source of air pollution emissions. Motor vehicle exhaust is a complex mixture, composition of which depends on fuel used, and type and operating condition of the engine – whether it uses any pollution control devices.
At present, motor fuels consists of Petrol, Diesel, LPG (mostly Butane) and CNG. In recent times, people have been very much successful in reducing motor vehicle pollutants; but due to enormous growth in population of vehicles on urban roads, the effectiveness of the new technology in reducing pollution is not very much relevant and practicable. Over the year, engine efficiency has also gradually improved with progress in Electronic ignition, Fuel injection systems and Electronic control unit; and so, the emission standards.
The major constituents of motor vehicle pollutants are 74% Carbon monoxide (CO), 16% hydrocarbon (HC), 8.5% nitrogen oxides (NOx), 0.8% particulate matter and 0.6% sulfur oxide (SOx).
* Carbon monoxide (CO): a product of incomplete combustion. Carbon monoxide reduces the human blood’s ability to carry oxygen and is dangerous to people with heart diseases.
* Carbon dioxide (CO2): It is well known that, carbon dioxide has very prominent role in global warming as a greenhouse gas.
* Hydrocarbons (HC): This is generated due to unburned or partially burned fuel and is a major contributor to urban toxic smog. They may cause lunge, liver damage and cancer to human being.
* Nitrogen oxides (NOx): These are generated when nitrogen in the air reacts with oxygen under the high temperature and pressure conditions inside the engine. NOx emissions contribute to both smog and acid rain.
* Sulfur oxides (SOx): Produced by combustion of petrol or diesel.
* Evaporative emissions: These are produced from the evaporation of fuel, and are largely contributor to urban smog, as these heavier molecules stay closer to ground level.
Thus, Motor vehicles contribute significantly to greenhouse gases but nevertheless the rise and rise of petrol, diesel and kerosene vehicles continues at an alarming rate. Experts say, if all vehicles were tuned correctly there would be up to:
(a) 16 per cent less tailpipe hydrocarbon emissions;
(b) 26 per cent less tailpipe carbon monoxide emissions;
(c) 9 per cent less nitrogen oxides emissions.
The expert study also revealed that, on an average, maintenance to polluting vehicles does not require the replacement of major or expensive parts. Tuning is mainly limited to the following: (a) replacing points and air filter; (b) replacing fuel filter (if necessary); (c) replacing oil and oil filter; (d) checking spark plug condition and gap—adjusting or replacing as necessary; (e) checking distributor condition and operation and adjusting as necessary; (f) checking and adjusting idle mix and speed; (g) checking and replacing spark plug and distributor leads as necessary; (h) checking and replacing hoses and other minor items in fuel/electrical/emission control system as necessary; (i) examining vehicle diagnostics and replacing faulty components.
Additional technologically advanced incorporated emission control systems may be used, such as: (i) Emissions control systems for engines using diesel, ultra-low sulfur diesel, bio-diesel, natural gas, or propane fuels; (ii) Selective Catalytic Reduction (SCR) technology to reduce NOx with the SCR Catalyst – mostly for stationary IC engines; (iii) Catalyzed diesel particulate filters to reduce Particulate Matters, CO and HC from diesel engines; (iv) Oxidation catalysts to reduce CO and HC emissions; (v) Three-way catalysts to reduce NOx , CO and HC emissions.
B. Factors to be considered for development of alternative & renewable fuel systems for motor vehicles:
It is known facts that, motor vehicle contribute adversely towards environment and causes significantly to increase greenhouse gasses. This picture is continuing alarmingly gloomier by the rise of petrol, diesel and kerosene vehicles. Not only do vehicles contribute net carbon gases, mainly CO and CO2, into the atmosphere which contribute to global warming and climate change but the products of combustion also produce additional local pollution causing many physical problems. Besides, the emission of nitrogen oxides, sulfur and carbon particulates (soot) can be very detrimental to health.
We now intend to discuss some imminent developments in running motor vehicles using renewable fuels / systems: We know that, fossil oil and gas are hidden treasures found in the earth crust. Therefore, these fuels are intrinsically cheap, requiring only the costs of finding and extraction from ground. There are three other features that make petroleum based fossil fuels such as petrol, diesel and kerosene uniquely attractive – (a) their very high energy densities, (b) the speed of recharging and (c) the existing world-wide distribution network.
(a) Energy densities are of prime important factor in choosing a particular system of energy-source in motor vehicles. To understand the system, let’s take few alternatives of new clean energy sources: (i) rechargeable electric batteries of lead-acid based; (ii) Lithium batteries; (iii) hydrogen gas and Fuel Cells (batteries energized by some form of hydrogen).
(i) Rechargeable batteries are relatively expensive and heavy (due to their low energy densities). Therefore, currently, they are not at all practicable in most of the cases. If we take a comparison between the energy stored per unit weight of petrol and lead-acid batteries the ratio would be about 500:1; even with nickel-metal hydride batteries (another possible contender), the ratio approaches 300:1.
(ii) Lithium batteries are emerging as a practical solution for commercial energy storage device for use in motor vehicles. It has an energy density some 30% to 60% higher than Nickel-Metal hydride, but the supply of Lithium batteries can make the system uneconomic.
(iii) Pure Hydrogen would be ideal, if it is derived in a sustainable way. Unfortunately, this is a gas we would be dealing with and so by definition it has a very low density. Extreme compression or cryogenic temperatures are needed to overcome this problem which poses lot of technological problems to be dealt with, and also the safety aspects. Fuel Cell technology is based on hydrogen, but experts say, liquid compounds containing hydrogen can be used instead of pure hydrogen. Such a system can, theoretically, match energy densities to those of the conventional combustion engine. Again, if using hydrogen means using petroleum compounds then its main advantage is lost.
(b) Speed of recharging is again a very important factor in selecting alternatives. The comparisons regarding speed of charging can be made very easily. How much time does a system take to recharge the vehicle in question in comparison to the time to fill the tank with petrol?
(c) Distribution network of conventional oil-based fuels is established world-wide as far the present system is concerned. For any alternative fuels it might take a longer time to build up such infrastructure for distribution.
C. Benefits and shortcomings of Battery operated Electric Motor Vehicles (EMV):
(a) Benefits of Battery operated electric motor vehicles are:
(i) Electric vehicles run on electricity generated from batteries do not emit air pollutants. Therefore, these vehicles are termed ‘zero emission vehicles’.
(ii) Within city, since most people drive vehicles less than 40 miles per day, electric cars are certainly practical for moving within a city.
(iii) Fossil fuel use in internal combustion engines give rise to various environmental problems and these problems may be solved by using battery operated electric vehicles.
(iv) Electric cars are more efficient than petrol / diesel driven vehicles in terms of performance per unit amount of money and yield better air quality.
(v) Decreased fuel costs for battery operated electric vehicles make them more cost-effective in the long run.
(vi) An electric car of today would only get better over time; as in near future the performance, cost and efficiency of batteries available would be much better.
(vii) In most of the case, driving an electric car is more smother and people feel very similar or better to driving a gasoline car.
(viii) Without the internal combustion engine, electric cars have the potential to be quieter and noise pollution is much less.
(ix) As the number of electric vehicle increases, number of recharging station will be more and drivers will be able to recharge their cars by plugging them in overnight to a recharging outlet or at home.
(x) Lot of research is going on for improving the battery size, battery life and recharging time for batteries; and in near future rapid developments could be seen in this respect.
(b) There are few shortcomings of electrically driven motor vehicles, which are mostly of battery related:
(i) While electric cars themselves are clean, but generating electricity to charge vehicle batteries produces air pollution and solid waste.
(ii) Potential health or safety risks associated with widespread use of electric vehicles have not yet been fully evaluated.
(iii) Many vehicle batteries contain toxic elements or produce toxic emissions which could make battery production, transport, use, and disposal a significant solid waste risks. We should try to use environment-friendly batteries.
(iv) People must consider how safely to dispose of or recycle these batteries. As current batteries are large and heavy, battery occupies large space leaving less room for cargo and passengers.
D. Options of various alternative fuels for motor vehicles:
We discuss below various other fuels that can be used as alternative to fossil fuel for motor vehicles; some of the fuels discussed are renewable:
(a) Bio-diesel: Motor vehicles can be very efficiently run by bio-diesel. Internal combustion engines are common in motor vehicles and are traditionally fuelled by diesel derived from fossil fuels. Thankfully diesel is a compound which can be replaced with bio-diesel which is an organically based product and is renewable. It is relatively easily produced from plant and animal oils, fats and greases. Environmentally, bio-diesel run vehicles also gives benefits in reduction of pollution.
(b) Liquefied Petroleum Gas (LPG): LPG is an alternative to petrol (gasoline), it offers lower local pollution levels than normal fuels. This fuel is compatible with petrol and many vehicles can run on either (dual-fuel vehicles); so the limited distribution of LPG is not a problem. Its main claims to fame are its reduced local pollution and it is also cheaper to run. Unfortunately, it is not renewable as it is petroleum based product and does not qualify for tackling climate change.
(c) Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG): In practice, LNG and CNG are replacements for petrol / diesel and suitable for heavier freight vehicles. Natural gas is intrinsically cleaner than petrol / diesel, but since it is a fossil fuel it is not renewable. It also contributes to global warming. At a local level it produces much less pollution than petrol or diesel and its use attracts financial incentives. The fuel tanks are specially designed for intense refrigeration (LNG) or high pressure (CNG) which makes them larger and heavier.
(d) Ethanol and Methanol: Can be used as alternatives or complements to petrol (gasoline) and can give less local pollution. If the raw source is petroleum then they are not renewable. Fortunately, they can be produced organically; e.g. from sugar cane etc., and then they can contribute in reducing climate change. Producing these alcohols organically can also bring economic benefits to rural developments by way of benefiting farmers.
(e) Hydrogen Fuel Cells: Fuel cells are not, strictly speaking, renewable or alternative energy, they are engines which convert energy; the energy source is actually hydrogen. Potentially this system can give clean and efficient energy. This technology is complex and research and development is needed to make them more feasible. The hydrogen fuel can be derived from a variety of sources. The hydrogen fuel cell is an electrochemical energy conversion device. Hydrogen and oxygen are fed into opposite sides of a cell, which are separated by a membrane permeable to hydrogen ions but not electrons. Hydrogen gas molecules entering the anode side of the cell are ionized in the presence of a catalyst to form protons and electrons. The protons pass through the membrane to combine with the oxygen and electrons to produce water at the cathode. The electrons flow through an external circuit from the anode to the cathode, creating an electrical current, which powers an electric load such as a motor. If the source of energy is renewable then we have a desirable situation but if it is petroleum derived, for example, and then it is not a renewable system. There are developments which indicate that fuel cells may provide an important source of energy in transport applications.
(f) Hybrid engine systems: This system uses internal combustion engines in tandem with battery-driven electric motors, to conserve energy. A few cars are now in production with this system. The batteries are charged from the kinetic energy of the vehicle (e.g., when braking). Manufacturers use Nickel-metal Hydride batteries (designed, it is claimed, to last as long as the car) and these are charged by the petrol power unit (via an alternator) during normal driving. Power is delivered to the wheels by either unit or both depending on the demands such as acceleration, during cruising or braking. Currently the vehicles are dearer, and this system only mitigates the problem of carbon emissions. It does not solve the emission problem. Nevertheless, the energy that is regenerated is truly green. One advantage of the electric system over the petrol engine is the torque available over a wide speed range; a normal car has several gears to narrow the speed range in use.
E. Environment-friendly Hydrogen gas as fuel in fuel cell and its challenges:
Hydrogen is the simplest and lightest element. Storage is one of the greatest problems for hydrogen. It leaks very easily from container meant for storage, no mater how strong and no matter how well insulated. Therefore, hydrogen in storage tanks always evaporates, at a rate of at least 1.7 percent per day.
Another important property of hydrogen is it is very reactive in nature. When hydrogen gas comes into contact with metal surfaces it decomposes into hydrogen atoms, which are so very small that they can penetrate metal. This causes structural changes that make the metal brittle.
One of the largest problems perhaps hydrogen fuel cell transportation has is its fuel tank size. In gaseous form of hydrogen, a volume of 238,000 litres gas is necessary to replace the same energy capacity of 20 gallons of petrol (gasoline). One option is to compress the gas. Because of gas’s low density property, compressed gas does not give a car as useful a as of gasoline as far as storage volume is concerned. Moreover, a compressed hydrogen fuel tank would be at risk of developing pressure leaks either through accidents or through normal wear and such leaks could result in dangerous explosions.
In case, the hydrogen is liquefied, the liquid hydrogen would give a density of 0.07 grams per cubic centimeter. In that case, it may require almost the four times volume of gasoline for a given amount of energy release. Besides, there are many difficulties in storing liquid hydrogen. Liquid hydrogen is cold enough to freeze air. Accidents may occur from pressure build-ups resulting from plugged valves. Besides, energy costs of liquefying the gas and refrigerating it also to be considered while calculating economy.
Other option may be considered is the use of powdered metals to store the hydrogen in the form of metal hydrides. The volume of stored metal hydrides would be little more than that of the metals themselves; but storing in this form, hydrogen would be far less reactive. However, the weight of the metals will make the storage tank very heavy.
As far as production of hydrogen is concerned, hydrogen does not freely occur in nature in useful quantities. Therefore hydrogen must be split from molecules, either molecules of methane derived from fossil fuels or from water. Currently, most hydrogen is produced by the treatment of methane with steam (the equation is CH4 (g) + H2O + e > 3H2(g) + CO(g)). The CO(g) in this equation is carbon monoxide gas, which is a byproduct of the reaction. Again the production of CO, which converts into CO2 is a greenhouse gas – not environment friendly option. Again, at present we do not have viable technology to obtain hydrogen from water, other than electrolysis – which is not energy saving option.
Therefore, as of now, it is a challenge before us to use hydrogen economically, efficiently and environment-friendly way. As lot research activities are going on in this field, very soon positive favorable result could be seen.
Principle of Hydrogen fuel cell:
The hydrogen fuel cell is an electrochemical energy conversion device. Hydrogen and oxygen are fed into opposite sides of a cell, which are separated by a membrane permeable to hydrogen ions but not electrons. Hydrogen gas molecules entering the anode side of the cell are ionized in the presence of a catalyst to form protons and electrons. The protons pass through the membrane to combine with the oxygen and electrons to produce water at the cathode. The electrons flow through an external circuit from the anode to the cathode, creating an electrical current, which powers an electric load such as a motor.
F. Environment-friendly Hydrogen Fuel Cell, its challenges and its efficiency:
Fuel cell is an electrochemical energy conversion device, wherein the electricity is directly produced by chemical reaction of fuel and an oxidizer. A fuel cell does not require recharging. The supply of fuel and oxidizer are to be continued as long as it is in operation. A fuel cell essentially consists of an anode—to which fuel such as hydrogen, ammonia etc., is supplied—and a cathode—to which an oxidant, commonly air or oxygen, is supplied. The two electrodes of a fuel cell are separated by a membrane of ionic conductor electrolyte.
A fuel cell is very similar to a battery in that it makes use of the energy stored in chemical substances. However, unlike the battery, in the fuel cell both the high-energy reactants and the low-energy products are not stored inside the cell. The reactants are supplied from outside the cell continuously and the products are removed from it once formed.
Probably the best-known type of fuel cell is hydrogen fuel cell that used in spacecraft. These cells react hydrogen and oxygen, forming water as they do so. The energy transferred from the hydrogen and oxygen in this process is collected as electrical energy rather than as heat. Fuel cells are compact and clean; the water produced by the fuel cells on the space laboratory used for drinking and washing purposes.
The hydrogen fuel cell is structured like a sandwich. At its core is a thin plastic foil – the proton exchange membrane (PEM), which is coated on both sides with a thin catalyst layer, preferably platinum (Pt), and a gas/permeable electrode out of a graphite paper. In the outer layers, gas channels have been milled into the two so-called bipolar flow field plates (FFP). Hydrogen flows through the channels on one side, while oxygen through those on the other side. Upon contact of the hydrogen with the Pt-catalyst, it causes the H-atom to ionize (to decompose into a proton H+ and an electron, e-). The positively charged protons permeate through the PEM membrane whereas the negative electrons do not. As a result of this diffusion process a voltage difference between the two electrodes out of graphite paper ensues. Attaching electrodes to the oppositely situated PME layers and connecting them via an external electrical load, the electrical gradient causing the electrons to flow through it, drive this load (e.g. DC motor). While the electrons are externally routed to the other side of the PME membrane, they join the oxygen, giving it a negative charge and finally merge with the protons that migrated directly through the foil. As a result of this electrochemical reaction, pure water (H2O) and a small amount of heat are formed.
Hydrogen and fuel cells have the potential to solve several major challenges facing the world today, i.e., increasing dependence on petroleum, poor air quality, greenhouse gas emissions and global warming. Many of the research programs are working the ways to accelerate the development and successful market introduction of these new exciting technologies.
Now the key challenges for commercialization of fuel cell and hydrogen infrastructure technologies include
(a) Fuel Cell Cost and Durability,
(b) Hydrogen Storage,
(c) Hydrogen Production and Delivery.
(d) Public Acceptance.
The efficiency of a fuel is dependent on the amount of power drawn from it. Drawing more power means drawing more current, which increases the losses in the fuel cell. As a general rule, the more power (current) drawn, the lower the efficiency. Most losses manifest themselves as a voltage drop in the cell, so the efficiency of a cell is almost proportional to its voltage. For this reason, it is common to show graphs of voltage versus current (so-called polarization curves) for fuel cells. A typical cell running at 0.7 V has an efficiency of about 50%, meaning that 50% of the energy content of the hydrogen is converted into electrical energy; the remaining 50% will be converted into heat. (Depending on the fuel cell system design, some fuel might leave the system unreacted, constituting an additional loss.)
For a hydrogen cell operating at standard conditions with no reactant leaks, the efficiency is equal to the cell voltage divided by 1.48 V, based on the enthalpy, or heating value, of the reaction. For the same cell, the second law efficiency is equal to cell voltage divided by 1.23 V. (This voltage varies with fuel used, and quality and temperature of the cell.) The difference between these number represents the difference between the reaction’s enthalpy and Gibbs free energy. This difference always appears as heat, along with any losses in electrical conversion efficiency.
Fuel cells are not constrained by the maximum Carnot cycle efficiency as combustion engines are, because they do not operate with a thermal cycle. At times, this is misrepresented when fuel cells are stated to be exempt from the laws of thermodynamics. Instead, it can be described that the “limitations imposed by the second law of thermodynamics on the operation of fuel cells are much less severe than the limitations imposed on conventional energy conversion systems”. Consequently, they can have very high efficiencies in converting chemical energy to electrical energy, especially when they are operated at low power density, and using pure hydrogen and oxygen as reactants.
In practice, for a fuel cell operated on air (rather than bottled oxygen), losses due to the air supply system must also be taken into account. This refers to the pressurization of the air and adding moisture to it. This reduces the efficiency significantly and brings it near to the efficiency of a compression ignition engine. Furthermore fuel cells have lower efficiencies at higher loads.
It is also important to take losses due to production, transportation, and storage into account. Fuel cell vehicles running on compressed hydrogen may have a power-plant-to-wheel efficiency of 22% if the hydrogen is stored as high-pressure gas, and 17% if it is stored as liquid hydrogen. Moreover, Fuel cells cannot store energy like a battery, but in some applications, such as stand-alone power plants based on discontinuous sources such as solar or wind power, they are combined with electrolyzers and storage systems to form an energy storage system. The overall efficiency (electricity to hydrogen and back to electricity) of such plants is between 30 and 50%, depending on conditions. While a much cheaper lead-acid battery might return about 90%, the electrolyzer/fuel cell system can store indefinite quantities of hydrogen, and is therefore better suited for long-term storage.
G. Hydrogen vehicles – future road vehicle system to tackle environmental problem:
Many vehicle manufacturers are currently researching the feasibility of building hydrogen cars, as more and more environment-friendly, clean, emission-free motor vehicles are needed to fight global warming. Hydrogen vehicles hold the promise of curing the world’s oil dependency while making transport-related air pollution and CO2 emissions history. But skeptics say that hydrogen is clean only if produced from renewable sources of energy.
a. Potential sustainable vehicle fuels – (i) Oil can not be expected as energy for sustainable transportation system due to its un-renewable. (ii) Renewable primary energy can not be used as vehicle fuel directly. (iii) Second energy carriers which have most promising sustainable “fuels” for vehicles are biomass fuel, electricity and hydrogen. In fact, combination hydrogen and electricity have been recognized by many manufactures for the best option for future road vehicle system.
b. Hydrogen has many benefits; such as (i) It is the most abundant element on earth; (ii) it is a versatile energy carrier that can be produced from any source of energy; (iii) it would reduce oil dependency, and bring transport-related air pollution and greenhouse-gas emissions to virtually none, and; (iv) it can be stored and easily kept over time.
c. A hydrogen vehicle is a vehicle that uses hydrogen for motive power. The power system of hydrogen vehicles converts the chemical energy of hydrogen to mechanical energy (torque). A hydrogen vehicle uses one of the following two methods for such conversion to mechanical energy,
(i) Combustion – In combustion, the hydrogen is burned in engines in fundamentally the same method as traditional gasoline cars.
(ii) Electrochemical conversion in a fuel-cell - In fuel-cell conversion, the hydrogen is reacted with oxygen to produce water and electricity, the latter of which is used to power an electric traction motor. This process is the reversal of the electrolysis of liquid water and should provide an open circuit voltage of 1.23 Volts per cell.
The fuel-cell conversion system in automobiles is preferred among above two systems. Because fuel-cell has advantages such as, large heat exchanger needed for fuel cells and their limited load change and cold start capability, they are certainly first choice as range extender for battery electric vehicles.
d. The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained through either of many (i) thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermal decomposition, or (ii) as a microbial waste product called bio-hydrogen or Biological hydrogen production.
Hydrogen can also be produced from water by electrolysis. If the electricity used for the electrolysis is produced using renewable energy, the production of the hydrogen would (in principle) result in no net carbon dioxide emissions and the process is renewable. Researches have been made successfully for on-board decomposition to produce hydrogen, when a catalyst is used.
e. Recent progress in R&D for hydrogen Fuel Cell Vehicle -
(i) Fuel cells stack power density improved by 20 times. Size and weight of fuel cell engine can be integrated in vehicle, nearly equal to diesel level.
(ii) Noble metal is used as the primary catalyst for fuel cells. In recent year, the amount of platinum usage has been reduced significantly by 10 times.
(iii)Power efficiency of fuel cell engine reaches to 45%- 50%, plus high efficiency of driving motor, therefore, power efficiency from tank to wheel is one time higher than petrol vehicle.
(iv) Reliability and durability of Fuel Cell Vehicles have been increasing as research inputs are flowing in.
f. Major challenges in development of hydrogen Fuel Cell Vehicle -
(1) Hydrogen produced from renewable energy: Great progress are being achieved in solar-hydrogen direct producing technology.
(2) Hydrogen storage: (i) Compressed hydrogen currently available to 700 Bar for longer range; (ii) Metal hydride storage weight rate 7%; (iii) Storage hydrogen by nano technology, such as nano fibers and tubes.
(3) Infrastructures: It is estimated that, quite large investment is needed in infrastructure for setting up large number of hydrogen fuelling stations. Experts predict that such investment in infrastructure would be returned in ten years.
(4) Competitive cost: Experts predict that, Fuel Cells stack cost would drop down to the almost same price of gasoline, 30 USD/kw by the year 2010.
H. Hybrid vehicle made urban transport system more fuel efficient with less pollution -
At present the road transport sector is the most polluting of all. It is generating more carbon dioxide (CO2) than electricity generation or the destruction of the rainforests. There are more than 600 million cars in the world today. In developed countries this number is set to double by 2015; and elsewhere in developing countries like China and India the increase will be even faster. Although the efficiency of operation of car engines manufactured has been substantially improved by incorporating better ignition management systems and the use of improved diesel engines; the tendency is still to build vehicles with performances much higher than the road conditions allow. Growth of population in developing countries resulted in congestion and pollution which is beginning to lead to a move towards electrical traction and an expansion of public transport systems, although people try to stick to the fictional “freedom” conferred by the private car.
In this context, development of fuel-cell-powered cars running on hydrogen fuel are quite encouraging, as are hybrid vehicles that use a small, optimized gasoline or diesel engine to charge a battery. Both the systems have demonstrated a good range and able to reduce pollution quite substantially.
a. As we discussed earlier some relevant aspects of hydrogen fuel-cell vehicle; we would now discuss about few points on hybrid system of vehicles as Hybrid vehicles are taking the auto world by storm. Ever since some of the Japanese auto manufactures (Toyota and Honda) introduced their hybrid vehicles into the marketplace, the demand has exceeded the supply. Most of those who have been attracted to the new lines of hybrid vehicles do so out of regard for the environment followed by a desire to lessen this country’s dependence upon foreign oil and save a few bucks on high gasoline prices.
b. A hybrid vehicle is a vehicle that uses two or more distinct power sources to propel the vehicle. Common power sources that hybrid vehicles are known today are ‘on-board rechargeable energy storage system (RESS) and a fueled power source either by internal combustion engine or by a fuel-cell’. Hybrid vehicle in general achieves greater fuel economy with lower emissions than conventional internal combustion engine vehicles. These favorable economic factors along with cleaner systems are primarily achieved by four elements of a typical hybrid design; such as, (a) Recapturing energy normally wasted during braking etc.; (b) Having significant battery storage capacity to store and reuse recaptured energy; (c) Shutting down the gasoline or diesel engine during traffic stops or while coasting or other idle periods; (d) Relying on both the gasoline (or diesel engine) and the electric motors for peak power needs, resulting in a smaller gasoline or diesel engine sized more for average usage rather than peak power usage.
These are the essential features that a hybrid vehicle has, which make it efficient in respect of fuel economy and providing emission-free environment for city traffic where there are frequent stops, coasting and idling periods. In addition, noise emissions are greatly reduced, particularly at idling and low operating speeds, in comparison to conventional gasoline or diesel powered engine vehicles. It may be important to mention here that, for continuous high speed highway use these features are much less useful in reducing emissions.
c. Another important aspect in hybrid vehicle is use of efficient battery. With the advent of new technology, more efficient batteries are made, which has made a hybrid vehicle more reliable. Today most hybrid vehicle use batteries that are made of nickel and lithium ion; these are regarded as more environmentally friendly than lead-based batteries used for most of cars today. Many of the manufactures claim that, even after use of hybrid car for about five years, no battery has been replaced. Hybrid technology for buses has seen increased attention since recent battery developments decreased battery weight significantly.
d. In short, the most advantageous factors in use of hybrid vehicles in city condition are:
(1) Improving fuel economy by (i) reducing wasted energy during idle/low output; (ii) recapturing waste energy (i.e. regenerative braking); (iii) reducing the size and power of the petrol / diesel engine, hence inefficiencies from under-utilization, by using the added power from the electric motor to compensate for the loss in peak power output from the smaller petrol / diesel engine.
(2) Durability and reliability of road transport is improved by (i) reduced wear on the gasoline engine, particularly from idling with no load; (ii) reduced wear on brakes from the regenerative braking system use; (iii) there’s no definitive word on replacement costs of the batteries because they are almost never replaced.
(3) The environmental impact of hybrid vehicles has been observed more favorable than any petrol / diesel engine vehicles. (i) Reduced noise emissions resulting from substantial use of the electric motor at idling and low speeds, leading to roadway noise reduction, in comparison to conventional gasoline or diesel powered engine vehicles, resulting in beneficial noise health effects. (ii) Reduced air pollution emissions due to lower fuel consumption, leading to improved human health with regard to respiratory and other illness. Pollution reduction in urban environments may be particularly significant due to elimination of idle-at-rest.
e. Now several transport system uses hybrid technology: such as (i) Motorcycles (ii) Automobiles and light trucks, currently number of manufactures in US, Japan and European countries produce hybrid electric automobiles and light trucks (iii) Buses (iv) Trucks (v) Military vehicles (vi) Locomotives (vii) Marine and other aquatic purposes.
I. Conclusion – Clean fuel vehicles are environmentally sound vehicles that replace traditional gasoline with clean fuels, thus providing a new approach for reducing air pollution from transportation systems. Improving vehicle efficiency is the single most effective means to reduce petroleum dependence. Many of the technological advances that led to today’s state of the art developments were in the areas of materials used in the fuel system to reduce evaporative emissions and corrosion caused by some fuels. Special fuel sensors were developed to aid in maintaining performance and making the transition from gasoline to the alternative fuel seamless in the operation and performance of the vehicle.
Moreover, developed nations and emerging economic nations must also focus on increasing their use of alternative fuels, including Biodiesel, Compressed Natural Gas (CNG), Electric Vehicles (EVs), Ethanol, Gas-to-Liquid Fuels (natural gas to diesel fuel), Hydrogen & Fuel Cell Vehicles, Liquefied Natural Gas (LNG), Liquefied Petroleum Gas (LPG / Propane) and LPG and CNG Conversions. Increasing the use of these fuels, however, faces significant uncertainties such as the availability of new vehicle technologies, the cost and availability of new fueling infrastructures, and acceptance of these fuels by consumers. While it is too early to predict what direction alternative fuel vehicles will take in the future, considerable work is underway in the areas of hybrid-electric vehicles, advanced battery development such as Lithium-Hydride, and fuel cells.