With pressure on operators to reduce pollution and cut their carbon output, what are the pros and cons of the alternatives to diesel power?
With concern over air quality and man-made global warming, there is increasing pressure from legislators and customers for vehicle operators to account for their emissions, and to reduce them wherever possible. The main areas of concern are nitrous oxides (NOx), hydrocarbon emissions (HC) and particulate matter (PM) – these can worsen air quality and have an effect on public health – as well as carbon dioxide (CO2), which is the main greenhouse gas associated with global warming.
Some cities are adopting ‘low emission zones’ (LEZs) which generally require vehicles with the latest emissions standards, while many firms are undertaking environmental audits, which usually focus on the net carbon production of the firm’s operations – its ‘carbon footprint’: fuel type and fuel usage are a large part of these audits.
More small companies are also undertaking green audits, particularly those in public sector work or facing eco-conscious consumers.
But these audits are about more than fuel: recycling is another issue, and while there are no current standards for commercial vehicle recyclability, it is worth noting that over 90% of an Iveco EcoDaily is recyclable.
The vast majority of commercial vehicles are powered by either compression-ignition (CI) diesel engines or spark-ignition (SI) petrol engines. Diesels are generally much more fuel-efficient than SI engines – so they emit less CO2 – but they tend to generate more NOx and PM.
Engine technology has improved dramatically, so that NOx, HC and PM emissions are all a small fraction of what they were twenty years ago. Driver aids such as stop/start systems and automated gearboxes can give significant fuel savings, while driver training is also a cost-effective way of saving fuel and thus reducing emissions.
But despite the increasing efficiency of diesel engines organisations are looking for power sources which improve air quality and reduce ‘carbon footprint’. However, all the alternatives are compromised in terms of range, performance or expense.
LPG (Liquefied Petroleum Gas) runs in lightly-modified SI petrol engines and generates low particulate emissions, but has no carbon benefit. It has attracted lower duty rates than petrol or diesel , but this advantage is steadily being reduced, and LPG is unlikely to be cheaper than other fossil fuels in the long term.
Natural gas (methane, CH4) is a clean-burning fuel which – for cars and vans – is used in SI engines and is suited to urban operations where air quality is paramount. It can be stored as CNG (compressed natural gas) or LNG (liquefied natural gas). CNG is stored in high-pressure steel or composite tanks. Even so, the ‘energy density’ of CNG is still lower than that of diesel fuel, so the tanks are bulky and range is compromised. There is a limited network of CNG filling stations in the UK, but the fuel is best suited to depot-based operations with a gas compressing plant (supplied with mains gas) on site. Some manufacturers offer CNG vehicles converted by a third party; Iveco offers a range of full factory-built CNG vans and trucks.
LNG is stored in insulated tanks at -160°C; again, the tanks are bulkier than diesel tanks, and operationally LNG vehicles are exactly the same as CNG vehicles. LNG filling tanks are easily installed at a depot, but there is again a limited network of LNG filling stations. None of the large manufacturers sells off-the-shelf LNG vehicles, but Iveco will convert CNG vehicles upon request.
Biofuels have been produced from plants or other biological matter, and they can be used without a net contribution to CO2 levels, making them ideal for minimising carbon footprint. They are also often usable as direct replacements for fossil fuels with no hardware modification. However, there is some concern over the sustainability of biofuel crops which take the place of food crops.
Biodiesel can come from plant crops or used cooking oils, and can be used as a diesel substitute or blended with mineral diesel to produce bio-blends B10, B30 etc. It represents an easy way to reduce a vehicle’s net carbon emissions. Before using biodiesel it is advisable to consult the manufacturer because acceptable levels vary greatly.
Biogas is natural gas (methane/CH4) produced in a ‘digester’ plant from vegetable waste, food waste and landfill rubbish. It is a direct substitute for CNG or LNG, and is sold at a small number of sites. Environmentally biogas is a good option. In the short term, it’s one of the best opportunities to get a good environmental result at the lowest cost.
Bioethanol is an alcohol fuel which can be used as a full or partial substitute for petrol – pure bioethanol has higher energy content than petrol.
Battery-powered electric commercial vehicles are well established: milk floats demonstrate quiet, reliable operation without local pollution – as well as short range, high weight and high purchase cost.
Modern electric vans are better, and are available at almost every size: Most manufactuers for example, make 3.5t and 5t GVW models. But they still have a major limitation: batteries are heavy and expensive, and to get significant range or performance the payload has to be reduced. An electric vehicle has a high upfront cost and it’s difficult to demonstrate a payback – you’ve got to have a low daily mileage to make them work. Electric vehicles are best suited for city applications.
While tailpipe emissions are non-existent, the electricity needed to charge the batteries has to come from somewhere – whether fossil fuel, nuclear or a renewable source.
Hybrid vehicles, typically with a diesel or petrol engine and a supplementary electric motor, can reduce tailpipe emissions dramatically – at low speeds, they often run on battery power alone – as well as saving fuel in stop-start operation. Range is not a problem, but as with electric vehicles the payback time is likely to be long.
Fuel cells are an alternative to battery power: they use a chemical fuel to generate electricity. The fuel is usually hydrogen (H2), which combines with oxygen to produce water. The Vauxhall Vivaro-e Hydrogen is an example of a fuel cell van being tested.
However, producing and storing hydrogen is problematic, so attention has moved to liquid-fuelled cells, typically using ethanol. This is an attractive solution, with no range limitation and potentially a small carbon footprint, but the vehicles will remain as prototypes for years to come.
