Annex A. Overview of clean technologies and fuels in the transport sector

This overview looks at buses that run on four major types of cleaner fossil fuels or other sources of power. These include compressed natural gas (CNG)/liquefied natural gas (LNG), liquefied petroleum gas (LPG), diesel with Euro VI engines and electricity.

For each fuel type we discuss the following:

• the main features of the fuel

• comparative advantages of the technology

• comparative drawbacks of the technology

• worldwide market penetration of the technology.

Table A.3 summarises the main points for each type of fuel.

Compressed natural gas vehicles

Description

Compressed natural gas (CNG) is a natural gas under pressure that remains clear, odourless and non-corrosive. Although vehicles can use natural gas as either a liquid or a gas, most vehicles use the gaseous form, compressed to about 218 kg/cm². CNG can be used as an alternative to conventional petrol and diesel fuels. Methane (CH₄) – which is the main component of CNG – is found above oil deposits or may be collected from landfills or wastewater treatment plants, where it is known as biogas.

It is stored and distributed in hard containers at a pressure of 20-25 MPa (Megapascals), usually in cylindrical or spherical shapes. Most natural gas comes from three types of wells: natural gas-and-condensate wells, oil wells and coal bed methane wells. Well-extracted natural gas requires treatment before it can be used in vehicles.

CNG is used in traditional petrol (internal-combustion-engine) automobiles that have been modified or in vehicles especially manufactured for CNG use, either with a dedicated system separate from the petrol system to extend range (dual-fuel), or in conjunction with another fuel, such as diesel (bio-fuel). CNG vehicles have been introduced in a variety of commercial applications, from light-duty trucks and sedans, like taxicabs; to medium-duty trucks, like UPS (United Parcel Service) delivery vans and postal vehicles; and heavy-duty vehicles such as transit buses, street sweepers and school buses.

CNG’s volumetric energy density is estimated to be 42% of that of LNG (because it is not liquefied; see Box A.1) and 25% that of diesel fuel.

Box A.1. A comparison of CNG and LNG

CNG and LNG are often confused. However, while both are stored forms of natural gas, the key difference is that CNG is stored as a gas at high pressure, while LNG is stored at a very low temperature, becoming liquid in the process. CNG is cheaper to produce and store than LNG, as it does not require an expensive cooling process or cryogenic tanks. CNG requires the use of very high pressures and a much larger volume of storage for the same mass of petrol. Therefore, natural gas is often transported over large distances in the form of LNG – in ships, trains or pipelines – and then converted into CNG before distribution to the end user.

Advantages

CNG combustion produces fewer undesirable gases than other fuels and is safer in the event of a spill, because natural gas is lighter than air and disperses quickly when released. In 2014, a comparison of Euro VI heavy-duty vehicles on CNG and diesel, conducted by the Danish Technological Institute,1 showed that CNG had a higher consumption of fuel but that NO_x emissions were lower. The levels of noise, CO₂ (contrary to other findings, see below) and particulate pollution were the same, however.

Natural gas is produced worldwide at a relatively low cost and is cleaner burning than petrol or diesel fuel. Natural gas vehicles emit on average 80% fewer ozone-forming emissions – i.e. carbon dioxide (CO₂) and nitrogen oxide (NO_x) – than petrol-powered vehicles. In addition:

• CNG does not contain any lead, thereby eliminating fouling of spark plugs

• CNG-powered vehicles have lower maintenance costs than other hydrocarbon-fuel-powered vehicles

• CNG fuel systems are sealed, preventing fuel losses from spills or evaporation

• CNG-powered vehicles are considered to be safer than petrol-powered vehicles

• CNG-powered vehicles produce less pollution and are more efficient.

CNG emits significantly fewer direct carbon emissions than petrol or oil when combusted. An engine running on petrol emits 22 kilograms of CO₂ per 100 kilometres, whereas a CNG-powered engine emits 16.3 kilograms of CO₂ per 100 kilometres. Therefore, switching to CNG can help mitigate greenhouse gas (GHG) emissions. However, natural gas leaks increase GHG emissions. The ability of CNG to reduce GHG emissions over the entire fuel lifecycle will depend on the source of the natural gas and the fuel it replaces.

Natural gas emits 30% less CO₂ per British thermal unit (BTU) than oil, 90% fewer particulates than conventional fuels, and fewer pollutants such as sulphur dioxide (SO₂) and nitrogen oxides (NO_x).

Drawbacks

The cost of fuel storage tanks is a major barrier to more widespread and rapid adoption of CNG as a fuel. Municipal governments are the most visible adopters of CNG technology in public transport vehicles, as they can more quickly amortise the money invested in the new (and usually cheaper) fuel. In other parts of the world, as the industry has expanded, the cost of fuel storage tanks has fallen.

CNG-powered vehicles require bigger fuel tanks than conventional petrol-powered vehicles. Since it is a compressed gas rather than a liquid like petrol, CNG takes up more space for each GGE (gasoline gallon equivalent).2 Usually, CNG tanks take up space in the trunk of cars or bed of pickup trucks modified to run additionally on CNG. This problem is solved in CNG vehicles that have factory-built tanks under the body of the vehicle, leaving the trunk free. Another option is roof installation (typically for buses), which requires attention to structural strength. Besides taking up space, tanks also add to the vehicle weight (especially when full). Rapid refuelling technology also requires expensive infrastructure investment and may lead to gas leaks.

Further, where an insufficient number of alternative fuel vehicles are in use investors may be reluctant to invest in infrastructure, while the manufacturing industry will not offer alternative fuel vehicles at competitive prices when demand is low because consumers are reluctant to buy them given the lack of an alternative fuel infrastructure.

Market penetration worldwide

CNG-powered vehicles are increasingly used in Iran, Pakistan and the Asian-Pacific region. India and China have witnessed rapid growth in recent years, and India, in particular, is forecast to become the world’s largest natural gas vehicle market (EC, 2016[1]), with their use especially common in New Delhi, and other large cities like Ahmedabad, Mumbai, Kolkata, Lucknow and Kanpur.

Their use is also increasing in South America, Europe and North America given rising petrol prices.

About 1.2 million vehicles run on CNG in Europe, but these represent only 0.7% of the European Union (EU)-28 and Switzerland’s vehicle fleet. Italy alone accounts for 75% of the market. More than 3 000 refuelling points are available, two-thirds of them in Germany and Italy. In total, 18 million CNG vehicles are in operation worldwide, representing 1.2% of the world’s vehicle fleet (EC, 2016[2]).

While the number of vehicles using CNG worldwide continues to grow steadily, alternative fuel vehicles in general only represented 3.4% of the European car fleet in 2012, and the use of alternative fuels in heavy-duty vehicles and maritime and aviation modes is negligible (EC, 2016[2]).

By 2025, LNG use in heavy-duty transport is expected to grow to 12 000 vehicles, mainly in Poland and Hungary. This is according to national plans submitted to the European Commission, which also foresee in total 431 refuelling stations and other infrastructure development in the EU – as a part of the Trans-European Transport Network (TEN-T) – to a total value of up to EUR 257 million by 2025 (T&E, 2018[3]).3

Liquified petroleum gas vehicles

Description

Also known as propane-butane mixture, liquified petroleum gas (LPG) is a flammable mixture of hydrocarbon gases used as fuel in heating appliances, cooking equipment and vehicles. LPG is prepared by refining petroleum (crude oil) or “wet” natural gas extracted from petroleum or natural gas streams as they emerge from the ground. It currently provides about 3% of all energy consumed worldwide, and burns relatively cleanly, without soot and very few sulphur emissions. As a gas, it does not pose ground or water pollution hazards, but it can contribute to air pollution. Further, its energy density per unit of volume is lower than either that of petrol or fuel oil, as its relative density is lower.

In some countries, LPG has been used since the 1940s as an alternative to petrol for spark ignition engines. In some cases, additives in the liquid extend engine life, and the ratio of butane to propane is kept quite precise in fuel LPG. Two recent studies have examined LPG and fuel oil mixes and found that smoke emissions and fuel consumption are reduced but hydrocarbon emissions are increased. The studies were split on carbon monoxide (CO) emissions, with one finding significant increases, and the other finding slight increases at low engine load but a considerable decrease at high engine load.

LPG has a lower energy density than either petrol or fuel oil, so the equivalent fuel consumption is about 10% higher. Many governments impose lower taxes on LPG than on petrol or fuel oil, which helps offset the greater consumption of LPG. LPG is the third most widely used motor fuel in the world after diesel and petrol. Estimates from 2013 show that over 24.9 million vehicles are fuelled by LPG worldwide. Over 25 million tonnes are used annually as a vehicle fuel.

Advantages

LPG is non-toxic, non-corrosive and free of tetraethyl lead or any additives, and has a high octane rating. It burns more cleanly than petrol or fuel oil and is especially free of the particulates present in the latter.

Commercially available LPG is currently derived mainly from fossil fuels. Burning LPG releases CO₂. The reaction also produces some CO. LPG does, however, release less CO₂ per unit of energy than coal or oil. It emits 81% of the CO₂ per kilowatt hour (kWh) produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid.

Other advantages of LPG include the following:

• LPG burns more cleanly than higher molecular weight hydrocarbons, because it releases fewer particulates.

• The inherent advantage of LPG over CNG is that it requires far less compression (20% of CNG cost), is denser (because it is a liquid at room temperature) and thus requires far cheaper tanks (consumer) and fuel compressors (providers) than CNG.

• Its advantages over petrol and diesel include cleaner emissions and less wear on engines than petrol.

Drawbacks

LPG main disadvantages may be summarised as follows:

• Safety: LPG is heavier than air, which causes it to collect in a low spot in the event of a leak, making it much more hazardous to use than CNG; more care is needed in handling.

• Environment: LPG is not as efficient or environmentally friendly as CNG and electric options for alternative fuels for buses.

• Technology: LPG provides less upper cylinder lubrication than petrol or diesel, so LPG-fuelled engines are more prone to valve wear if they are not appropriately modified.

Market penetration worldwide

LPG is currently the most adopted alternative fuel in road transport in terms of number of vehicles. The LPG market is dominated, in terms of vehicles, by five countries, which together account for almost half of global consumption: Turkey (4 million vehicles), the Russian Federation (3 mln), Poland (2.8 mln), Korea (2.4 mln) and Italy (2 mln) (EC, 2016[1]).

However, LPG is losing momentum in the European Union, United States and Japan, because compared to electric mobility and even CNG, its environmental benefits over conventional fuels are limited. However, LPG is still promising in developing markets in China, India and the Russian Federation.

Diesel vehicles with Euro VI engines

Description

Petrol and diesel remain the most common fuels for all vehicles.

Biodiesel – which is increasingly being used in diesel engines – is brought to the market mainly via blending with conventional diesel. The largest market is the European Union (EU), followed by the United States and Brazil. Biodiesel does not, however, reduce NO_x emissions from vehicles, which is an increasing focus of attention for cities.

US regulations attempting to reduce the impact of these fossil fuels on the environment have mandated the supply of ultra-low sulphur diesel and the use of ethanol (also known as E85) in petrol.

Table A.1 and Table A.2 contain a summary of the EU emission standards that apply to diesel buses. They show two different types of testing requirements: 1) steady state testing (Table A.1), which lists emission standards applicable to diesel (compression ignition – CI) engines only, with steady-state emission testing requirements; and 2) transient testing (Table A.2), which lists standards applicable to both diesel and gas (positive ignition – PI) engines with transient testing requirements.

Table A.1. EU emission standards for heavy-duty diesel engines (steady-state testing)
Tier	Date	Test cycle	CO	HC	NOx	PM	PN	Smoke
			g/kWh				1/kWh	1/m
Euro I	1992 < 85 kW	Economic Commission for Europe of the United Nations (ECE/UN) Regulation-49	4.5	1.1	8.0	0.612
	1992 > 85 kW		4.5	1.1	8.0	0.36
Euro II	October 1996		4.0	1.1	7.0	0.25
	October 1998		4.0	1.1	7.0	0.15
Euro III	October 1999 Enhanced environmentally friendly vehicles (EEVs) onlyb	European Stationary Cycle (ESC) and European Load Response (ELR)	1.5	0.25	2.0	0.02		0.15
	October 2000		2.1	0.66	5.0	0.10 - 0.13a		0.8
Euro IV	October 2005		1.5	0.46	3.5	0.02		0.5
Euro V	October 2008		1.5	0.46	2.0	0.02		0.5
Euro VI	31 December 2013	World Harmonized Stationary Cycle (WHSC)	1.5	0.13	0.4	0.01	8.0x1011
Note: aPM = 0.13 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3 000 min-1; b EEV is a European emissions standard for buses and trucks (> 3.5t in the category M2 and M3). Vehicles equipped with EEV engines exceed the emission quality of the Euro 5 standard applicable to all new vehicle types from 1 September 2009 on trucks and buses.
Source: (DieselNet, 2016[4]), “EU: Heavy-Duty Truck and Bus Engines: Regulatory Framework and Emission Standards”, www.dieselnet.com/standards/eu/hd.php (accessed 30 March 2017).

Table A.2. EU emission standards for heavy-duty diesel engines (transient testing)
Tier	Date	Test cycle	CO	MNHC	CH4a	NOx	PMb	PNc
			g/kWh					1/kWh
Euro III	October 1999 Enhanced environmentally friendly vehicles (EEVs) only	European Transient Cycle (ETC)	3.0	0.40	0.65	2.0	0.02
	October 2000		5.45	0.78	1.6	5.0	0.16d
Euro IV	October 2005		4.0	0.55	1.1	3.5	0.03
Euro V	October 2008		4.0	0.55	1.1	2.0	0.03
Euro VI	31 December 2013	World Harmonized Transient Cycle (WHTC)	4.0	0.16e	0.5	0.46	0.01	6.0x1011
Notes: a – for gas engines only (Euro III-V: NG only; Euro VI: NG + LPG).
b – not applicable to gas-fuelled engines at the Euro III-IV stages.
c – for diesel engines; particle number (PN) limit for positive ignition engines to be defined.
d – PM=0.21 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3 000 min-1.
e – total hydrocarbon content (THC) for diesel engines.
Source: (DieselNet, 2016[4]), “EU: Heavy-Duty Truck and Bus Engines: Regulatory Framework and Emission Standards”, www.dieselnet.com/standards/eu/hd.php (accessed 30 March 2017).

Advantages

The main advantages of shifting to diesel buses with Euro VI engines include:

• The purchase price of modern diesel-fuelled engines is typically lower than moving to cleaner technologies (such as LPG or CNG).

• The need for additional investments in the vehicle itself or in supporting infrastructure is not as great as for LPG and CNG, which often require vehicle modifications or supporting infrastructure (such as specialised filling stations or maintenance centres).

• A standard diesel city bus delivers lower carbon emissions per passenger than a standard car and CO₂ emissions can be achieved by encouraging more passengers to shift to public transport.

Drawbacks

The main drawbacks of introducing diesel buses with Euro VI engines are:

• The shift from Euro V to Euro VI for heavy-duty vehicles will require considerable investments by manufacturers and public transport operators undertakings and huge outlays from bus manufacturers.

• They cause significant harm to the environment, in the form of particulate matter (PM) from engine exhaust.

Market penetration worldwide

Diesel engines are globally one of the most common choices for combustion engines for buses and other commercial vehicles. For the time being, diesel and biodiesel buses constitute by far the greatest part of the bus fleet (90% of the bus fleets in Europe, according to the results of the 3iBS survey, which surveyed 70 000 buses operated in 63 European cities and regions) (UITP, 2015[5]).

Electricity-powered public transport

Description

The electrification of road transport is expanding in Europe driven by the need for clean public transport, which is encouraging manufacturers to develop new models.

Trams are one of the oldest means of public transport and their popularity has come and gone depending on the country. But recently many cities seeking sustainable urban development are reintroducing tramways into the urban space.

Trolleybuses have followed a similar evolution, and are also experiencing an upsurge in popularity. Their main advantage over trams is that they require no battery or special rail infrastructure (overhead wires are less expensive to construct than rails), and they are also quieter. On the other hand, trolleybuses can be hybridised to run “autonomously” using an on-board battery.

In this context and as the result of technological changes and improvements in vehicle efficiency, all-electric buses are a new strategic means for achieving greenhouse gas mitigation targets (and need even less infrastructure than trams or trolleybuses). The technology is still not as mature as diesel buses, but it is on the way to market maturity. This is confirmed by the increasing number of pilots and plans (Vienna, Berlin, Paris, London, Stockholm, China) that are emerging.

There are several sizes of electric buses to be found on the market, depending on demand and needs. While electric mini and mid-size buses already exist, larger (>10m) buses are still being developed.

With this technology, in addition to transport capacity, it is important to consider vehicle autonomy and charging technologies (i.e. charging at the bus depots or on-board along the bus route).

"Traditional" cable charging takes place at night, after the daily service is complete. It is usually done on normal recharge, so as not to disturb the electricity network. A further possibility is to integrate a fast-charging solution at the end of the line, in order to guarantee continuous operation of the service. This technology has been adopted in Vienna (Austria) – the batteries charge in 10 to 15 minutes and last for 120 to 150 kilometres.

On-board "flash charging" technology allows buses to connect to the charging point on an overhead high-power charging contact when they pull into selected stops, topping up the batteries while passengers get on and off. This very fast charging mode is already used in Geneva (Switzerland) and at the airport of Nice (France).4

A similar technology is the pantograph, already used by trains and tramways. For buses, this charging mode can be used at bus stops, at end stops or in depots. A bottom-up pantograph is mounted on the bus roof. The charging procedure starts as the pantograph is raised and comes into contact with the mast pantograph, centred above vehicles’ front axle reference position. Several cities – e.g. Gothenburg (Sweden), Namur (Belgium) and Vienna (Austria) – have started adopting this technology.

Induction may become the technology of the future for charging vehicles. When the bus stops at a station equipped with a recharge system buried underground, the on-board charging coil lowers and power transmission can begin. Charging only lasts for the time the passengers get disembark and embark and can restart again at the next station, offering unlimited autonomy. Berlin is the first capital city to adopt this wirelessly charged e-bus line.

Advantages

Electric vehicles offer several advantages over conventional internal combustion engine vehicles:

• Less dependence on oil.

• Lower greenhouse gas emissions and air pollutants when using electricity from “low-carbon” sources of power (Box A.2).

• They are more efficient and better at converting energy from batteries into moving the vehicle than the conventional internal combustion engine. They also recover energy while braking, thus reducing total energy consumption.

• Less noise pollution.

• Significant savings can be made over the lifetime of the vehicle because although investment is higher, the costs of fuel (electricity) and maintenance are lower than for an internal combustion vehicle.

• When the battery has lost some of its capacity it can be used for other purposes, such as for storing renewable electricity that can help regulate the power grid and the development of renewable energy.

Box A.2. How clean is electricity production?

Electricity is an energy carrier that can be converted domestically from a wide variety of primary energy sources. When electricity is produced from renewable energy sources, this can offer a nearly zero-emission well-to-wheel pathway, although this is not always the case (e.g. when a combination of renewable and non-renewable sources is used). Electricity will continue to become increasingly low-carbon as the power sector continues to reduce carbon intensity.

Drawbacks

• The development of electric vehicles depends mostly on the price of the vehicles and their battery (which can be expensive) as well as on the battery performance and energy autonomy.

• Electric buses are more expensive than diesel-powered vehicles, however, over their lifespan the total costs of electric buses are lower.

• Investment in new infrastructure in addition to the bus and battery is needed. The cost varies according to the system chosen and the number of charging points.

• The power grid must be made compatible with the energy requirements of a fleet of vehicles at economically acceptable costs.

• Electric buses can have a negative impact on the environment depending on the battery technologies, resource extraction and cell production processes, as well as the type of electricity production, and how they are disposed of at the end of their lives (e.g. recycling).

Market penetration worldwide

The number of electric buses increased tenfold between 2014 and 2016, reaching a global stock of about 345 000 vehicles in 2016. China leads in the use of electric buses, with more than 343 000 units in operation, followed by Europe with only 1 273 vehicles.

Nevertheless, only 3% of the worldwide bus fleet is currently electric. The increase in the stock does suggest that the market is moving beyond the demonstration phase into commercial development, however.

Table A.3. Comparison of fuels for urban public transport
Parameter	CNG	LPG	Diesel EEV
Purchase cost (diesel = 100 baseline)	120	110	100 (higher than traditional diesel)
Fuel type	Natural gas		Diesel
Range (km)	300	500	750
Consumption per 100 kilometres	60-70 m3	36 kg	40-50 l
Operating costs	+	+	++
Re-fuelling time	Long; 3-6 hours	Quick (minutes)	Quick (minutes)
Re-fuelling complications	Average (compression)	Very high (liquefaction, storage)	Low
Noise	Low	Low	Low
Pollution	Low emissions of particulates, SO2, NOx. Nearly zero contribution to smog	Low emissions of particulates, SO2, NOx, nearly zero contribution to smog	Lower emissions than traditional diesel. Higher emissions than CNG and LPG
Use	Small/medium buses	Large buses	All types
Other opportunities and advantages	Fuel can also be made from biomass or landfill gas.	Low temperatures in winter support LNG storage
Other challenges and disadvantages	Heavy fuel tanks and buses with higher clearance required Dedicated refuelling stations required (for example, at bus depot) Dedicated workshops required Rapid refuelling requires expensive infrastructure investment and may lead to gas leaks	Limited storage time for LPG (buses have to be constantly used, and after five days without use require venting) Fuel is transported and stored at low temperature Requires complicated installations for cleaning and liquefaction at stations	New norms (such as Euro VII or Euro VIII) may impose stringent quality requirements

References

[4] DieselNet (2016), “EU: Heavy-Duty Truck and Bus Engines: Regulatory Framework and Emission Standards”, DieselNet website, http://www.dieselnet.com/standards/eu/hd.php (accessed on 30 March 2017).

[1] EC (2016), Alternative Fuels and Infrastructure in Seven Non-EU Markets – Final Report, European Commission, Brussels, http://ec.Europa.eu/transport/themes/urban/studies/doc/2016-01-21-alternative-fuels-and-infrastructure-in-seven-non-eu-markets.pdf.

[2] EC (2016), Clean Transport – Support to the Member States for the Implementation of the Directive on the Deployment of Alternative Fuels Infrastructure: Good Practice Examples, European Commission, Brussels, http://ec.Europa.eu/transport/themes/urban/studies/doc/201.

[16] EU (2014), “Directive 2014/94/EU of the European Parliament and of the Council of 22 October 2014 on the deployment of alternative fuels infrastructure”, Official Journal of the European Union L 307/1 of 28 October 2014, pp. 1-20, http://data.europa.eu/eli/dir/2014.

[3] T&E (2018), CNG and LNG for vehicles and ships – the facts, European Federation for Transport and Environment, Brussels, http://www.transportenvironment.org/sites/te/files/publications/2018_10_TE_CNG_and_LNG_for_vehicles_and_ships_the_facts_EN.pdf.

[5] UITP (2015), Bus Systems in Europe. Towards a Higher Quality of Urban Life and Reduction of Pollutants and CO2 Emissions, UITP Position Paper, International Association of Public Transport, Brussels, https://www.uitp.org/sites/default/files/cck-focus-papers-files/UITP_PositionPaper_Bus%20Systems%202015.pdf.pdf.

Notes

← 1. See Danish Technological Institute on emissions reduction: www.dti.dk/specialists/emission-reduction/37141 (accessed 20 March 2017).

← 2. GGE is the amount of alternative fuel it takes to equal the energy content of one liquid gallon (ca. 3.785 litres) of petrol. GGE allows consumers to compare the energy content of competing fuels against a commonly known fuel, petrol. GGE also compares petrol to fuels sold as a gas (natural gas, propane or hydrogen) and electricity.

← 3. According to Directive 2014/94/EU on the deployment of alternative fuels infrastructure, natural gas (CNG and LNG) and liquefied petroleum gas (LPG) are considered as alternative fuels in addition to electricity, hydrogen, biofuels (as defined by Art. 2 of Directive 2009/28/EU), and synthetic and paraffinic fuels (EU, 2014[16]).

← 4. See new generation of buses: http://new.abb.com/grid/technology/tosa; and autonomous electric buses in France: www.avere-france.org/Site/Article/?article_id=5730 (accessed 26 April 2017).

Annex A. Overview of clean technologies and fuels in the transport sector