|2006 IPCC Sector categorization|
|Energy supply and consumption (excl. industry)|
|Use of primary energy sources|
|Large scale - short term|
|Renewables and fossil fuels combined|
|Transport: vehicle and fuel technologies|
This article describes a broad range of vehicle and fuel technologies for motorised transport that are currently available or in development. Their characteristics, advantages and disadvantages are outlined, with particular attention to the rate of fuel consumption (sometimes referred to as the efficiency) and the carbon content of the fuel. Both of these underlie the carbon emissions of a motorised vehicle. The article outlines the major technologies being contemplated for both vehicle and fuel
technologies. This article does not provide exhaustive coverage of the range of available options or of issues to be considered, but it should provide a useful introduction to drive train and fuel technology options.
All technologies discussed within this article are feasible and reasonable to consider for implementation, being either mature technologies, in the process of being implemented, or under serious consideration for implementation in the short term.
Traditionally petrol or diesel fuelled engines have underpinned mechanised transport with over a billion such vehicles on the road today. The automotive industry has responded with a well accepted move towards smaller, more efficient engines and towards the use of more efficient diesel. Responses to regional or global issues have meant that some technologies have achieved market penetration in the past few decades, for example, simple engine technologies like CNG and LPG conversions, or more recently some biofuels. Some have achieved a degree of market acceptance, for example, hybrid, e-hybrid and full electric vehicles, while others have held promise for a long period but have yet to achieve any market share at all, such as hydrogen fuel cell vehicles.
Selection of appropriate vehicle and fuel technologies should depend, not only on greenhouse gas impact
and the matter of oil depletion, but also on a variety of other factors, including the following:
Mass movement versus flexibility
The choice of transport technology initially depends on the population density. In urban areas the population density and thus demand for freight and passenger services ensures mass movement in trains, light rail and buses is viable. On the other hand, wealth creation enables more private vehicle ownership, which may add to congestion and other poor transport outcomes. In rural areas low population densities limit viable mass transport options and thus may favour the more flexible of these options such as buses.
Energy infrastructure: investment needs, competition and energy security
Fuel delivery systems depend on long supply chains and complex life cycles for each stage of the process. For example, the life cycle for the energy extraction stage of the supply chain includes: exploration, technology development, construction, production and decommissioning of exhausted energy resource fields. There are similar life cycles for conditioning and conversion of the raw products. As well as these stages, the supply chain also includes: transport (sometimes on a global scale); secondary conditioning and conversions (such as at petroleum refineries); distribution and tertiary processing; delivery of final products to retail outlets; and, finally, use by end consumers.
The traditional delivery systems are those for petroleum fuels, electricity and fossil based natural gas.
These delivery systems represent a vast investment. This includes investment in the education of designers, installers, maintainers and energy users, which is important for the safe implementation and use of new transport energy and vehicle support systems.
Traditionally, interaction between these three vastly different systems has provided a level of competition and a high degree of energy security. A reduction in the viability of a delivery system, for example, away from oil distribution as oil costs increase, will lead to increases in energy supply risks and reduced regional resilience. Both for transport needs and general power supply a more resilient and diverse set of energy options is advantageous.
Incremental investment for transport use is that which adds to existing energy and vehicle infrastructure, for example, extra investment in oil, electricity and natural gas systems. On the other hand, the complete overlay of a new infrastructure with related fuel production and supply and vehicle technology, such as that needed to implement hydrogen fuel cell vehicles, will require significant investment. No country in the industrialised world has made significant inroads into replacing distribution systems associated with petrol and oil, but that is the challenge that needs to be faced in the next few decades. Several emerging economies are making such changes as set out below.
Range versus efficiency
The need to store fuel on-board most vehicles imposes some limitations. The key trade-off is between the range of the vehicle (how far it can travel on a tank of fuel) and how much fuel it may economically store on-board.
A vehicle that has to travel for significant distances or times between refuelling opportunities needs to carry more fuel. On the other hand, the urban private vehicle environment requires less storage of fuel due to easier access to refuelling and, at most times, less distance covered.
Electric vehicles clearly target this latter market. There are many electric bicycles and small passenger cars available to meet short urban travel requirements.
Due to its energy density, natural gas fuel on-board storage combined with vehicle hybridisation is now
able to directly compete with current petrol ICE based ranges without the fuel taking up too much space.
This is the most difficult task ahead for more climate friendly fuels such as hydrogen and electricity that at
present cannot provide such competition. An internal combustion engine can drive up to 40 times further
than an electric vehicle per kg of energy stored with technology available today (Birch, 2010).
Maturity of underlying technologies
Current transport technologies are changing fastest in the passenger vehicle market, which will eventually be reflected in road-based freight vehicles. The technical options are multiplying for both engines and fuel, without any obvious winner. What appears clear is that regions will have the opportunity to influence and guide technical options in order to meet their own requirements.
All options for vehicle technology are subject to intense innovative efforts and incremental improvements. Such is the pace of innovation that most technological opportunities are nowhere near their full potential, including:
- the aforementioned hybridisation, with the potential to change many aspects of the industry
- battery research and development (This continues to promise an impressive rate of improvement in both energy density and resilience.)
- the incumbent internal combustion engine technology, which is similarly responding to the competitive environment and decreasing environmental impacts
- fuel cell technology coupled with natural gas, methanol and hydrogen, which continues to make steady progress
- the simplicity of micro turbines, which have not as yet fully tested the market
- natural gas (methane) technologies, which are achieving a renewed level of interest due to:
- the relatively recent expansion of known world reserves through unconventional resources
- widespread deployment of distribution networks for homes and industry, which make it suitable for easy transition to transport applications
- a wide diversity of regional reserves
- the emerging promise of renewable natural gas.
In this state of flux, it is important to ensure that a roadmap for the development of regional transport options is robust enough to take advantage of this rate of development, but doesn’t head down a dead end with any individual technology.
Global industry versus regional needs
Both the fuel supply and vehicle supply industries are global and well entrenched. It can take significant effort to get these large suppliers to change and adapt to a regional need (Mikler, 2010).
Vehicle cost and social and environmental impact
The Nano, reputed to be the world’s cheapest production car, is produced by Tata for its home market in India. When it was launched it was selling for about US$2500 equivalent, about half the cost of its nearest rival, and a lot less than most other vehicles (Wells, 2010).
From an owner or driver’s perspective, the purchase of such a car may be driven by aspirations of status and power, mobility needs and possibly safety. However, it generally adds a significant financial burden to owners through fuel and maintenance costs, and in most Indian cities may not get them to their destinations any faster.
On a societal scale, its introduction may increase national fuel consumption, put stress on fuel supply chains, emissions, repair and maintenance systems, and road infrastructure requirements.
Thus it is clear that there are important social and environmental issues to be considered when the increasing affluence of a community and the continually reducing vehicle costs meet to enable wider private vehicle ownership.
New automotive technologies in combination with a variety of new fuels are capable of delivering significant benefits to any society seeking to create a more resilient transport system with lower carbon impacts. Developing countries that are growing have the ability to make such changes through judicious choice of fuels and technologies related to their local resources and needs. A variety of technologies vie for market share. Long term, the fuel cell in combination with a variety of feeder fuels may gain market share. In the short to medium term electric and hybrid technologies will provide substantial benefits, especially when coupled with renewable sources of fuel. In the face of energy infrastructure constraints, biofuels, renewable electricity and renewable natural gas enable a clear path forward.
Drive train technology: spark ignited internal combustion engines
This engine type powers the vast majority of vehicles on the world’s roads, and is particularly suitable for scooters, motorbikes, cars and smaller vehicles. It is perhaps the most versatile of engines, and may be configured to operate on a range of fuels, including petrol, LPG, natural gas and ethanol.
This technology is one of the least efficient at converting fuel to mechanical energy, with typical automotive efficiencies being about 15-20%. Practical peak efficiencies at best can be about 32% (Wu & Ross, 1997).
This is a mature mass produced and economic technology. Most drive train innovation is designed to replace this technology. See also: 'Direct injection for internal combustion engines'.
Drive train technology: compression ignition internal combustion engines
This engine powers the majority of heavier duty vehicles such as trucks, buses and trains. Its key characteristic (compression ignition) limits the fuels on which it operates, primarily to diesel, but enables a significant increase in efficiency to around 22-28%. Its peak operating efficiency is about 43% (Cuddy & Wipke, 1997).
Recent, but as yet uncommercialised, technical development is enabling this engine type to operate on other fuels, such as petrol, LPG and natural gas, at nearly equivalent efficiencies (Osborne et al., 2001).
A mature truck and bus market ensures it is a mass produced and economic engine, whilst its rapidly expanding small vehicle market is driving down production costs.
Drive train technology: micro turbines
Micro turbines are an emerging internal combustion technology, very similar to its much larger technological cousin the combined cycle gas turbine for city wide electricity production. Its key advantage is simplicity, in that it has few moving parts, and may provide competition to the spark and compression ignition engines. Its peak efficiency at about 26% is normally combined with the advantages of hybrid technologies. There is no evidence of wide scale commercial production.
Drive train technology: fuel cells
Fuel cell technology has more in common with the electric battery than the internal combustion engine it competes with. It uses an electrochemical process instead of a thermal one to convert its fuel to electricity, and some heat. In recent years it has been linked with hydrogen as its primary fuel source, though with on-board convertors, other fuels including methanol and natural gas have proved technically effective and easier to provide.
Its efficiency at 36% is high, and its on-board emissions of oxygen, water and little else is attractive at first glance, though the source and derivation of its fuel impact heavily on its overall environmental credentials (Von Helmolt & Eberle, 2007; Ewan & Allen, 2005; Mueller-Langer et al., 2007).
There is currently no mass produced vehicle, though extensive demonstrations have occurred with passenger cars and buses. There remains some question about the timing of realistic commercial scale vehicular fuel cells. See also: 'Fuel cells for mobile appliations'.
Drive train technology: batteries and electric motor vehicles
The technology involves charging a battery on board the vehicle and using this stored electricity to drive electric motors which in turn drive the wheels.
The on-board efficiency - up to about 85% - of this technology is the highest of those contemplated and on-board emissions are virtually eliminated. However, like the fuel cell, the source and delivery of the electricity determines the overall efficiency and environmental impact of the technology, including its greenhouse credentials.
Global manufacturers are now beginning to mass produce for the passenger car market (Ribeiro et al., 2010). Mass transit vehicles already in use include light and medium rail trains and some battery electric buses. See also: 'Electric vehicles'.
Drive train technology: catenary electric motors
In some circumstances catenary (wire) fed electricity may be used with electrically powered vehicles. This provides all the advantages of electric vehicles without the problems of battery installations. Typically metro medium duty rail systems operate with this type of technology as well as trolley buses and most new intercity fast trains.
Drive train technology: hybridisation
Many passenger vehicle manufacturers are now delivering or about to deliver hybrid technology in their vehicle offerings, as noted for electric vehicles previously. It involves the installation of an electric motor drive and battery system in combination with a fuel source and/or engine. The primary advantages of hybridisation include:
- enabling the internal combustion engine to operate at its peak efficiency all the time. Operating at peak efficiency will increase the range and decrease the impact of emissions of greenhouse gases in comparison to traditional internal combustion engine (ICE) configurations for all vehicles
- the ability to turn off the engine at idle and at other inefficient times
- the recapture of energy expended in accelerating the vehicle and in navigating hilly terrain (regenerative braking)
The regenerative braking capacity is most effective in stop/start traffic or rolling hills. It will not work so well on extended climbs and descents, or for rural trips, as the battery required for this would be otherwise too large. Diesel/electric hybrid technology is in common use in freight rail as its preferred motive option. See also: 'Hybrid electric vehicles', 'Plug-in hybrid electric vehicles'.
Fuel choices: fossil fuels
Traditionally oil has driven the world’s transport needs, but as the world has realised that it is a finite commodity, other sources of energy from fossil fuels have emerged. Though the International Energy Agency state ‘The world’s oil resource base is sufficient to meet demand until 2030, although the cost of supply will increase’, other sources already referenced in this section note that peak oil may have already occurred, with peak natural gas and coal to follow in the first half of this century.
The bench mark against which all fuels and related technology are measured is petrol and diesel, which have very high energy content per unit of weight compared to almost any other fuel. Figure 1 indicates the relative energy content of a variety of fuels, benchmarked against petrol. Thus diesel may be considered to have about 20% more energy per unit volume than petrol, whilst batteries have only 2% of the volumetric energy content of petrol in its current compressed storage format. Greenhouse gas emissions from fossil fuels can be reduced through efficiency improvements, the most significant of which may be hybridisation.
Fuel choices: natural gas
Traditionally fossil natural gas systems have played an important role in general energy supply. It is a versatile fuel, being a feed for electricity production, a source of thermal heat, and a transport and storage medium.
Although there is much debate as to how long natural gas reserves will last, it is touted as a bridging fuel to a renewable future (Flavin & Kitasei, 2010). Natural gas’s versatility sees it being advocated as an economic and clean replacement for coal and nuclear power. It produces up to 54% less greenhouse gas than coal.
It also has a significant and growing infrastructure base in many economies. Its wide availability and reliability of supply in most urban areas provides many oportunities to extend its use beyond domestic, commercial and industrial energy supply to include transport.
By far the major source of natural gas is from fossil gas and oil fields, but unconventional sources such as shale and coal seam gas are having a big impact on supply. On a small scale, biogases are currently produced from municipal waste sites, and liquid manure is a very environmentally beneficial source, as use of either also alleviates greenhouse gas emissions to the atmosphere, not just by replacing the more intensive greenhouse gas producing fuels of petrol and diesel, but also enabling the natural gas to be burnt rather than being emitted directly to the atmosphere with its multiplier impacts. Methane emissions have around 21 times more greenhouse impact than carbon dioxide by volume, hence its release to the atmosphere should be avoided.
Larger scale direct production of renewable natural gas (methane) from solar, algae, or other similar renewable sourceis now becoming attractive, primarily for its:
- environmental benefits
- capacity to act as a storage medium as well as an energy carrier
- pre-existing handling, transport and storage infrastructure
- relative energy density in comparison to other alternatives such as hydrogen and batteries
- compatibility with current and future internal combustion technologies.
Production of renewable natural gas also acts as a carbon sink for sequestration of carbon dioxide, much the same as plantation timber (Fujita & DuBois, no date).
In the following review of the other alternative fuels, it is noticeable that many are derived from natural gas, which means that their energy efficiencies are always less than that of the original natural gas. See also: 'Compressed natural gas (CNG) in transport' and 'Liquid Natural Gas (LNG) in transport'.
Fuel choices: LPG
Liquid petroleum gas (LPG) is a relatively internationally tradeable automotive fuel mix of propane and butane, generally used for light duty vehicles such as passenger vehicles. It is sourced from either natural gas production facilities, where the propane and butane occur naturally within the feedstock gas in small quantities, or from the fossil oil refining process. It is used as a domestic heating source in many countries which do not have access to natural gas, as it is more easily transported in smaller quantities. See also: 'LPG in transport'.
Fuel choices: synthetic diesel
Synthetic diesel is a diesel replacement manufactured from either coal or gas with technology dating back to the 1930s in Europe.
Natural gas is generally the feedstock of choice due to its yield, availability and process simplicity compared with coal. Natural gas to synthetic diesel has a poor conversion efficiency (the amount of energy in the end product divided by the amount of energy in the feedstock), in the range of 60 - 65%. Coal to synthetic diesel has efficiencies significantly less than even this (CONCAWE, 2006). Countries that are vulnerable to oil imports have resorted to synthetic diesel but it is not a long term solution due to its reliance on limited supplies of coal and gas based fossil fuels, poor conversion efficiencies and poor climate change outcomes.
Fuel choices: biodiesel
Biodiesel is a fuel manufactured from a variety of biomass sources, the major ones being rape sunflower seed and woody products. The woody production process is similar to that for synthetic diesel, though it is less efficient. In most cases biodiesel can be used as a substitute or blend for diesel fuel.
The advantage of biodiesel from a climate change point of view is that, though the biodiesel emits carbon dioxide at the point of combustion, the biomass sources used in its manufacture recapture an equivalent amount during growth, so the overall lifecycle carbon account is almost zero.
Regional differences in sourcing the biomass may bring its production into competition with natural biodiversity or other uses of biomass products, including carbon sequestration and food production. See also: 'Biodiesel'.
Fuel choices: ethanol
Ethanol may operate as a minor substitute for petrol in most vehicles, and in many places is limited to about 10% of the petrol mix. Where specifically adapted vehicles are available this proportion can be increased to about 85%.
Ethanol is generally manufactured from biomass - either directly from crops such as sugar cane and beet, or indirectly from grains such as corn, rye, wheat and barley. Agricultural residues, forestry residues, grasses, municipal wastes and plantation trees can also be used. Some believe that these cellulosic sources rather than the direct sugar sources will form the backbone of supply in the future due to food security conflicts.
Like biodiesel, the overall life cycle emissions of ethanol for greenhouse gases are virtually zero. Also like biodiesel, regional differences in sourcing the biomass may bring its production into competition with natural biodiversity and other uses of biomass products including carbon sequestration and food production. See also: 'Bioethanol from sugar and starch-based crops'.
Fuel choices: electricity
Electricity is an exciting new frontier for some parts of mainstream automotive use. It is generally used in either a dedicated battery electric vehicle or, in more recent times, an e-hybrid, a vehicle using both the plug-in electricity supply and more conventional fuels to share the task of providing energy for the vehicle. It is also used in mass transit systems such as metropolitan medium and light rail systems. Like natural gas, its wide availability and reliability of supply in most urban areas provides many opportunities to extend use beyond its traditional role in buildings to include transport.
Electricity sources are extensive and diverse, and range from coal and natural gas to nuclear and renewables. Its primary advantages include zero on-board fuel based emissions, though the energy efficiencies of, and emissions from, its production and transmission to the vehicle must also be considered. Electric vehicles section highlights its use in transport. See also: 'Electric vehicles'.
Fuel choices: hydrogen
Hydrogen is not yet in commercial use within the transport industry. The technology of choice for this fuel is the fuel cell, because of its on-board efficiency. It holds promise as a renewable ‘energy carrier’ as it may be produced from a vast range of original energy sources. The primary form of production today is from natural gas. It can also be produced from biomass, including algae (for which current research is indicating promising results), or from solar directly, through electrolysis of water (Bartels et al., 2010; Milbrandt & Mann, 2007). Electrolysis, like electric battery systems, is heavily dependent on the source of the electric power used in its production for its environmental performance.
The implementation of this technology is likely to be revolutionary, effectively overlaying a complete and new energy delivery system on a scale and timeframe unprecedented in modern times. Its maturation as a viable technology may take some time and will be highly dependent on significant research and development. As there are no pre-existing storage and distribution systems for hydrogen, costs for infrastructure may significantly outweigh costs of the vehicles and fuels and therefore serious reconsideration of the ‘hydrogen economy’ is occurring.
Fuel choices: Dimethyl Ether (DME)
Dimethyl ether (DME) is a colourless liquid or compressed gas traditionally used as an aerosol and normally produced from either natural gas or coal, though it may be manufactured from renewable sources such as woody biomass. It has the advantage of being more energy efficient to produce than synthetic diesel (CONCAWE, 2006).
Some early work suggests it may also be used as a blend with diesel with some environmental benefits. It is primarily used to reduce dependency on LPG, and it requires a transport infrastructure similar to that for LPG. As with all biologically derived fuels, regional differences in sourcing the biomass may bring its production into competition with natural biodiversity or other uses of biomass products including carbon sequestration and food production.
Fuel choices: methanol
Methanol in some cases can be used as a substitute or blend for petrol, although its future transport use may be as an energy carrier for fuel cell vehicles. Its use in conventional vehicles has diminished to the stage where few current vehicles can operate on it.
Methanol is a colourless liquid energy primarily manufactured from natural gas or coal to be a feedstock for the manufacture of MTBE, a petrol additive which benefits the combustion process. Depending on the original energy source, the greenhouse balance of methanol can vary from extremely poor (coal base) to very good (biomass black liquor base) (CONCAWE, 2006).
A 2007 estimate indicates worldwide annual consumption of about 1,300 billion litres of petrol and about 1,400 billion litres of diesel, the majority of which is used to fuel the 1 billion vehicles on our roads. The following provide examples of nations changing their fundamental transport mix to ease away from dependence on oil and limit greenhouse gas emissions from transport.
Over the last two decades a variety of countries such as Argentina, Pakistan, Iran and Brazil have shown how to diversify the supply chain for fuels, with natural gas in use in Argentina, Pakistan and Iran, and both natural gas and the biofuel ethanol in Brazil. Pakistan, Italy, Argentina and Brazil have successfully implemented after-market vehicle conversions with natural gas. China is also making significant progress, leapfrogging some of the current technologies to join in the production of newer ones (Zhang et al., 2009).
The compression ignition internal combustion engine’s efficiency and recent advances in small high speed versions has enabled it to supplant the petrol option in passenger vehicles in the industrialised countries, particularly in Europe and more often now in Australia and the US. Natural gas is currently used as a fuel in about 10 million vehicles worldwide, the majority in Argentina, Brazil and Italy.
Reputedly the vehicle LPG market has grown from about 7 million vehicles worldwide in 2000 to about 13 million today. Major users include South Korea, Australia, Italy and Japan.
The European Union is producing up to 7 billion litres of biodiesel annually. Plants are primarily located in Germany, Italy, Austria, France and Sweden, whilst the USA produced about 1.3 billion litres in 2009 (up from 38 million in 2001).
The USA consumed about 41 billion litres of ethanol in 2009, replacing about 28 billion litres of petrol. The European Union produced about 3.7 billion litres in 2009, primarily in France, Germany and Spain, with a further 1.7 billion litres capacity under construction. The EU production sources are generally from cereal crops and waste biomass.
In more recent times some countries such as China have been using DME as a blending agent or substitute for LPG.
Germany and the US are planning complete development of new transport infrastructure with hydrogen and fuel cell technologies supplemented by biomass fuels competing directly with diesel and petrol systems. They are implementing the first stages of an entirely new vehicle technology and supply infrastructure within their communities.
The capacity of developing societies to further advantage their economies through their fuel and related automotive industry is also demonstrated by Brazil, which – using its local market, location, alliances, indigenous fuel supply (natural gas and biofuels), resources, and labour market – has over more than a decade become a regional hub for automotive supply, producing approximately 3 million vehicles in 2009 (Da Cruz & Rolim, 2010).
Judicious choice of fuels and drive train technology may have a significant impact beyond the direct benefits of more effective transport and the reduction of greenhouse gas emissions. The emissions described in the environmental benefits section below create smog and impact on population health through respiratory related diseases (asthma and infection), and through other serious health problems such as liver disease and cancer caused by noxious emissions.
Fuel is a significant component in the whole-of-life cost of a vehicle. Increased efficiency reduces the burden this places on the owner and on the economy as a whole. In many cases transport fuel is an imported commodity and thus can place a significant strain on the national balance of payments. Use of more local fuel sources reduces this impact. Reductions in local pollution and greenhouse gases from the use of these fuels and technologies also have economic benefits. The adaptation of appropriate technologies to suit regional circumstances may also lead to development of new industry.
Airborne transport emissions can have a detrimental environmental impact apart from climate change. They can be generated at the vehicle exhaust, at the power station or at production facilities. The technologies described in this section can have positive environmental benefits including the reduction of:
- airborne emissions such as particulates, nitrous oxides, carbon monoxides and other organic compounds generated by many fuels
- acid deposition, which causes infrastructure degradation and may lead to acid rain;
- soot deposition on both natural and human infrastructure.
Similarly emissions from many of the liquid based fuels contaminate wetlands and groundwater resources.
Local supply of fuel also reduces the impact of production and transport of fuels over vast distances and from increasingly more difficult locations that have resulted in disasters such as the Exxon Valdes and the Gulf of Mexico drilling rig.
The implementation of these drive train and fuel technologies, if done successfully, can significantly reduce the greenhouse impact of a growing transport sector. However, poor implementation may also lead to increased greenhouse gas production, for example, liquefied hydrogen fuel cell transport based on coal fired electrical supply will significantly increase overall emissions. Immediate support for smaller vehicles based on natural gas or diesel instead of petrol can have some impact, but hybridised vehicles will have a considerably larger impact. In the longer term renewably supplied natural gas and electricity offer the opportunity to virtually eliminate greenhouse gas emissions.
Carbon emissions from the variety of fuels, their sources, and vehicle technologies vary considerably. Figure 4 below indicates the relative carbon emissions of a select range of fuels. The vertical axis shows both the fuel type and its source, whilst the horizontal axis shows emissions of carbon dioxide from each of these as a percentage of emissions from conventional petrol with current drive train technology.
For example, both petrol with optimised technologies (striped graphic) and diesel (white graphic) are represented using a full hybrid technology optimised for fuel efficiency. The only exceptions to this (included purely for comparative purposes) are conventional petrol and diesel matched with current technologies, indicated with the black and ‘diamond’ graphics respectively. In figure 4 the combined fuel type and source, selected as representative fuels, are ranked from least emitting at the bottom to most emitting at the top.
Key points to note include:
New drive train technologies for conventional diesel and petrol fuels will make a significant difference in the carbon emissions of vehicles in comparison to conventional technologies of today.
The relative efficiencies gained through the use of diesel continues to outperform that of conventional petrol, even under optimised technologies, justifying the continued drift towards diesel in industrialised countries’ passenger car markets.
The wide diversity of outcomes possible from ethanol, DME, synthetic diesel, hydrogen and electrical supply is based entirely on the source of the original energy, and the efficiency of production and conversion processes. If managed well, all such fuels and technologies can significantly reduce the greenhouse gas emissions due to mobility, but if handled poorly can increase them. For example, the implementation of a hydrogen fuel cell program based on liquefied hydrogen and derived from coal shows a greenhouse gas impact in the order of 271% of the current and conventional petrol based Drivetrain, a poor result, whilst fuel cell vehicles fuelled by hydrogen derived from a central production facility using wind powered electrical energy supply and piped to site will produce a greenhouse impact of only 5% of that of conventional petrol, a well managed outcome from this perspective.
Natural gas fuel generally outperforms petrol and diesel in almost all circumstances and in its renewable form can be carbon neutral. In special cases natural gas, along with some other energy carriers, may actively reduce the overall carbon load.
For complete replacement of petrol and diesel with ultra low or zero net carbon emissions the clear options are renewable electricity, natural gas or hydrogen. Ethanol and DME are generally used as a blend with conventional fuels, and hence may not completely replace them.
The following briefly outlines the incremental costs of each fuel and drive train option when compared with its traditional petrol equivalent. A small proportion of the passenger and commercial vehicles sold annually may meet ‘value’ market requirements, such as the aforementioned Nano, and most operate only on traditional petrol and diesel fuels. More buyers are choosing diesel vehicles. These tend to be slightly more expensive than petrol equivalents, and the diesel fuel price is also trending upward as a result of this increasing demand.
Most current vehicles may also be able to operate on biofuels such as ethanol mixes or biodiesel at little or no additional cost.
Electric vehicles are generally more expensive, with those currently in production for the motor vehicle market being targeted at the Northern consumer and typically costing in the order of 20-50% more than their ICE equivalent, typically about US$30,000 or more each.
On the other hand electricity is one of the cheapest and most efficient ways of transporting and acquiring energy. This of course is highly dependent on tariffs on, and subsidies provided to, the various fuels, which vary from country to country.
Alternative fuel vehicles are common in the passenger vehicle market, with factory fitted and commercial pre- and post-market conversion technology available for LPG and natural gas adding some capital cost. In most Northern societies this typically amounts to US$500-4,000, and such conversions are popular where local fuel supplies and/or government incentives allow them.
The use of gaseous fuels, primarily natural gas, to replace diesel fuel is more commercially difficult for larger vehicles such as trucks and buses. Depending on supplier and technology, these technologies add between US$5,000 and 100,000 to the cost of a diesel equivalent vehicle.
Hybrid electric vehicles fall somewhere between the traditional IC powered vehicle and the electric vehicle in terms of capital cost, and may be closer to the electric vehicle when it comes to operational costs.
Fuel cell based vehicles on the other hand are currently both very expensive to buy (if commercially available) and very expensive to operate, particularly with regard to fuel supply and maintenance.
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