Biofuels for road transport

By Dr David Martin

Ecovector Consulting

June 2009

Why are biofuels of interest?

“Biofuels” is the generic term used for transport fuels derived from crops. There are three main types of biofuel:
  • Biodiesel – is currently made mainly from oily crops such as oil seed rape or used vegetable oils. These oils are processed using esterification to produce a fuel which is similar to mineral diesel, and can be used as a substitute or blend with mineral diesel in conventional diesel engines;
  • Bioethanol – is currently made from starchy crops such as sugar cane, wheat or other cereals. The production process involves fermentation of plant materials that are rich in sugar or starch with additional hydrolysis steps enabling fermentation of forestry and cellulose-based wastes. The fuel can be used as a substitute or blend with petrol;
  • Biomethane – is the product of anaerobic digestion of organic wastes such as animal manures or food residues. The gas produced from the digestion process is upgraded to 95% methane content and then can be used as a fuel in vehicles designed to operate on compressed natural gas (CNG).
Biofuel technology has been around as long as the combustion engine, but recent concerns about fuel security, climate change, and the wish to support rural economies has led to market encouragement and support by Governments around the world. Biofuels in principle are low in life cycle greenhouse gas emissions compared with fossil fuels and offer an indigenous source of fuel. These properties are important in addressing two issues in energy policy, namely climate change and the need to reduce transport carbon emissions, and the need to reduce dependency on oil imports. In 2003, against a backdrop of grain mountains and payments to farmers for set-aside land, the European Union approved the Biofuels Directive. Under this directive, Member States agreed to set indicative targets for biofuels use and to promote their uptake. As a result in the UK, fuel duty incentives and other measures to stimulate the use of biofuels have been introduced by the Government.

Oil seed rape is a common feedstock for biodiesel:

photo: © David Martin

What is happening in the UK?

The Renewable Fuels Agency (RFA) was set up by the Government to implement the Renewable Transport Fuel Obligation (RTFO), which came into force in April 2008. The RTFO now obliges fossil fuel suppliers to ensure that by 2010 biofuels account for 3.5% by volume of the fuel supplied on UK forecourts. The purpose of the RTFO is to reduce the UK's contribution to climate change and its reliance on fossil fuels. As well as obliging fuel suppliers to meet targets for the volumes of biofuels supplied, the RTFO requires companies to submit reports on the carbon emission savings and sustainability of the biofuels. It is administered by the RFA. Under the RTFO suppliers are required to report on the carbon emission savings and sustainability of the biofuels they have supplied. Suppliers that do not submit a report will not be eligible for RTFO certificates; suppliers will however at this stage be able to report unknown biofuel origins, carbon savings and sustainability, in recognition of the difficulty of obtaining this information in the context of existing supply systems. It is unlikely that reporting 'unknown' will remain acceptable as the system moves to mandatory sustainability standards in the future. The RFA will publish reports comparing the performance of different suppliers and the biofuels they have supplied, and expect consumers to be interested in using these comparisons to inform purchasing choices. Fuel suppliers have been given a detailed methodology for calculating the carbon savings of a variety of biofuels and there is a meta-standard approach to sustainability reporting by which fuel suppliers can report and provide evidence that they meet a benchmarked list of existing agro/environmental standards.

How can we use biofuels?

Whilst very few vehicle manufacturers have designed vehicle engines that can operate on pure biofuels, liquid biofuels can be used in low concentration blends (5-10%) with petrol or diesel without engine modification. Liquid biofuels are an obvious alternative fuel since they can be blended with petrol or diesel and used in a conventional internal combustion engine. They generally have slightly lower energy densities than petrol and diesel, such that they offer a lower range when used in high blends. Once produced, liquid biofuels are relatively easily storable and transportable and can use the existing petrol/diesel infrastructure, with blending facilities added on.

Biodiesel generally has a lower volumetric energy density than mineral diesel, which results in biodiesel vehicles requiring more fuel/kilometre. Bioethanol has a high octane rating enabling high engine compression ratios that increase engine efficiency and performance. However, compared with petrol, bioethanol has a low volumetric energy density that results in bioethanol vehicles also requiring more fuel/kilometre. These fuel efficiency penalties are not significant at the low concentration blends currently used.

Most vehicle warranties are still only valid for use with biofuel blends of up to 5%. This is because of concerns about technical issues such as cold starting problems of biodiesel, and incompatibility with certain types of elastomers and rubber components. Bioethanol can also cause corrosion problems with engine materials, and is difficult to vaporize at low temperatures. However, high concentrations of liquid biofuels (for example with bioethanol up to 85%) can be used in specially adapted vehicles, and some manufacturers are offering these vehicles on the market.

A significant recent advance is the development by companies such as Saab and Ford of flexible fuel vehicles that are able to operate on a range of petrol-bioethanol blends up to 85%. The engine management system automatically detects which fuel is being used and adjusts the timing accordingly. One example is the flexible fuel Ford Focus:

photo: © David Martin

Biomethane can be used in the same vehicles as use compressed natural gas. The three main vehicle technologies that are used for these gas vehicles are:

  • Bi-fuelled vehicles – comprise a spark ignition engine that is fitted with both a gas and a petrol fuelled system, so that the vehicle is capable of operating on either fuel;
  • Dedicated gas vehicles – use a spark ignition engine that suns solely on gas and has been optimized for this purpose. This technology is frequently used in heavy-duty vehicles, and replaces a conventional diesel engine;
  • Dual-fuel vehicle – using a compression ignition diesel engine that runs on a mixture of gas and diesel, typically 70% and 30% diesel.
Biomethane can be stored on the vehicle at high pressure in gaseous form in specially designed tanks, in exactly the same way on compressed natural gas can be used. An alternative is to store the gas in liquefied form by cooling and then compressing the gas, which is again stored in high pressure tanks at a low temperature on board the vehicle. This process increases the amount of fuel that can be stored in a given volume. At present, the availability of biomethane for transport purposes in the UK is very limited.

The VW Caddy EcoFuel has been developed to operate on CNG, but could also operate on biomethane:

photo: VW web site

What are the Greenhouse gas emission benefits?

Biofuels can offer CO2 savings compared with petrol and diesel. These savings vary widely depending on feedstocks used, farming method and production technique. While CO2 emissions from the tailpipe are exactly offset by those absorbed in the growing of feedstocks, there can be CO2 emissions associated with farming (particularly the use of fertilizer) and the production process. Moreover there are severe adverse climate change impacts if forest or grassland is cleared to provide land to grow feedstocks, because large quantities of CO2 “locked-up” in the plants and soil are released. Biofuels offer some security of supply advantages in reducing dependence on oil-rich regions of the world. However, major dependence on biofuels could leave fuel supply exposed instead to agricultural risks such as weather, including floods and drought, and pests and diseases; as well as creating pressures on food supply.

The life-cycle emissions of biofuels vary significantly depending on how and where the fuel is produced. For example, in Europe, bioethanol from sugar beet can have life cycle emissions that are up to 70% lower than conventional petrol, although many lower-cost bioethanol pathways provide much smaller CO2 savings. Bioethanol from Brazilian sugar cane can provide savings of at least 80%. In general, the main sources of emissions from liquid biofuels are from gaseous oxides of nitrogen emissions associated with fertilizer use, and fossil energy used in processing. Biomethane from organic waste can actually have negative life cycle emissions compared to a do-nothing scenario where, when left to decompose, the waste emits methane into the atmosphere (which is 21% more potent as a greenhouse gas than the CO2 emitted when burning the fuel).

Most biofuels appear to offer at least a small CO2 saving, compared with petrol and diesel, on a year-by-year basis. However, if forest or grassland is converted to accommodate their production, there can be very large one-off releases of CO2. For ease of calculation, life-cycle studies of biofuels generally assume no land-use change, but this can be a dangerous simplification. Moreover, even excluding land-use change impacts, there is continuing uncertainty over the life cycle calculations for biofuels.

What about the indirect effects of biofuels production?

In the last 2-3 years, there has been growing concern about the role of biofuels in rising food prices, accelerating deforestation and doubts about the actual benefits in reducing greenhouse gas emissions. This has led to serious questions about their sustainability and extensive campaigns have been run by environmental groups against higher targets. Concern was further raised among policy makers when work in the US indicated that US biofuels production on agricultural land displaced existing agricultural production, causing land-use change leading to increased net greenhouse gas emissions.

The Gallagher review was prepared in July 2008 for the UK Government in response to these concerns . Its purpose was to examine the scale of the indirect effects of current biofuels production, and to propose solutions. The review concluded that there is a future for a sustainable biofuels industry but that feedstock production must avoid agricultural land that would otherwise be used for food production. This is because the displacement of existing agricultural production, due to biofuel demand, is accelerating land-use change and, if left unchecked, will reduce biodiversity and may even cause greenhouse gas emissions rather than savings. The Government agreed that the introduction of biofuels should be slowed in the UK until adequate controls to address displacement effects are implemented and are demonstrated to be effective. A slowdown could also reduce the impact of biofuels on food commodity prices, notably oil seeds, which have a detrimental effect in developing countries.

What does the future hold?

The expansion in biofuel production across the world has also stimulated research and development into 'second generation' fuels. These advanced biofuels are not yet commercially available, but offer the prospect of better environmental performance and of using a wider range of feedstocks, including additional wastes. Second generation biofuels can be made from a wide range of feedstocks including the non-food parts of crops (e.g. straw); dedicated energy crops (e.g. poplar, switchgrass and jatropha); agricultural waste; municipal waste and even algae. The importance of non-food feedstocks in expanding biofuel production in a sustainable manner is recognised, and is the subject of much ongoing research.

Scientists working as part of the new £27M Biotechnology and Biological Sciences Research Council Sustainable Bioenergy Centre, launched early in 2009, will investigate how to maximise the yield of non-food energy crops such as willow so that sustainable bioenergy replacements for fossil fuels become a reality:

Photo: Biotechnology and Biological Sciences Research Council

In future, improved biofuels technology could significantly reduce the life-cycle emissions of biofuels, by allowing the crop itself to provide energy for production and by using feedstocks that require little or no fertilizer. This could deliver CO2 savings of 80-90% compared to petrol and diesel, although cost is currently a barrier. In addition future biofuels could potentially offer significantly reduced land requirements, lowering the risks associated with land-use change.

As an alternative to fossil fuels in the road transport sector, biofuels remain a potential option for the future. However, other alternative systems, such as electric plug-in vehicles, diesel/electric hybrid vehicles, and hydrogen fuel cell vehicles are being developed by manufacturers. Whilst these alternatives may also have their technical or environmental difficulties, it seems that the future direction of transport fuels technology remains unclear.

Where can I find further information?

Renewable Fuels Agency
Low Carbon Vehicle Partnership
Biomethane for Transport
Renewable Energy Association
Energy Saving Trust
King Review of Low Carbon Cars
Locations of biodiesel filling stations
British Sugar information about bioethanol
Saab information about bioethanol
Second generation biofuels