A guide to green car types

Modern diesel cars

Surprisingly enough simple diesel cars offer some of the ‘greenest’ cars available on the market at the moment. Compared to petrol cars, diesel vehicles have significantly lower CO2 emissions per kilometre travelled because of the higher efficiency of diesel engines. Diesel vehicles also emit lower levels of hydrocarbons (HC) than equivalent petrol vehicles. However diesel engines emit greater levels of NOx (Nitrous Oxide) and particles than new petrol vehicles.

LPG

LPG, also sometimes know as autogas produces fewer emissions than petrol and diesel but fuel consumption is worse. It has been popular in the past due to its cheaper cost; it retails for roughly around half the price of petrol and diesel. However there are not many cars that are LPG ready, a conversion costing around £2000 is necessary for most vehicles. It has a simple chemical make-up meaning LPG produces significantly less carbon monoxide, hydrocarbons and oxides of nitrogen emissions as well as a smaller percentage of carbon dioxide emissions than petrol. LPG also emits 90 per cent less particulates, in weight, than diesel engines. LPG is also a natural by-product of gas production meaning that there is a plentiful supply. However there are limited numbers of service stations from which you can refill. From an environmental view point, LPG will quickly evaporate in the event of a fuel spill meaning that unlike petrol and diesel, there little risk of ground or water contamination. It also offers a quieter ride, noise levels are around 50 per cent quieter than diesel engines. There are other fuels that can be used in an alternative combustion engine to provide a substitute to conventional petrol and diesel such as compressed natural gas (CNG), Coal-to-Liquid (CTL), Biomass-to-Liquid (BTL) and a whole host of biofuel related sources such as rapeseed or palm oil.

Hybrid

Hybrid cars offer reduced fuel consumption over conventional engines therefore reduce localised emissions. There is no compromise on performance because a hybrid car such as the famous Toyota Prius has a conventional petrol engine with the addition of a nickel-hydride battery. Hybrid petrol-electric cars have an electric motor which provides the power at low speeds and move to petrol for driving at higher speeds. They therefore achieve the best fuel economy in urban driving rather than on a motorway run. The batteries are recharged while driving and hybrids use regenerative braking, meaning that energy is put back into the battery when braking, again improving energy efficiency. Hybrid diesel-electric is still under development but will achieve even better fuel economy.

A second generation of rechargeable hybrid cars which use more advanced lithium batteries would allow hybrid vehicles to run longer on solely an electrical source. The new lithium batteries are also lighter and hold their charge better than the hydride batteries, however the second generation is not yet widely available.  

Electric

Electric engines are directly free of emissions therefore useful for reducing localised air pollution, unfortunately most of UK electricity is produced from burning fossil fuels so electric vehicles aren’t really emission free as they are often proclaimed. Most electric vehicles are very limited in speed and can only make around 60 miles before needing recharging. There are more advanced models such as the Tesla Roadster which can travel around miles 244 on a single charge to a top speed of 125 mph. Unfortunately these cars are not cheap, the Roadster costs around $109,000! Battery technology is improving all the time though as lithium batteries begin to replace lead-acid ones, offering reduced weight and improved driving range.

Hydrogen and fuel cells

Hydrogen technology has often been tipped as the alternative fuel of the future. The emissions are clean since hydrogen vehicles only emit water. The current generation of hydrogen cars use a hydrogen storage tank and a fuel cell stack. The hydrogen is therefore industrially produced prior to storage, usually through steaming natural gas meaning that it does have a carbon footprint. In the car, the hydrogen is combined with atmospheric oxygen in the fuel cell to produce water and electricity to power the vehicle. The Honda FCX Clarity is the first hydrogen car to be mass produced but is not yet available in the UK. Honda claims that the FCX Clarity has about 2-3 times the fuel economy of a petrol-powered car, and 1.5 times that of a petrol-electric hybrid vehicle, of comparable size and performance. The Clarity has a range of around 270 miles on a single tank.

Second generation hydrogen cars will have on-board hydrogen production although this may be a long way off. Currently the biggest problem is the infrastructure to support the operation of hydrogen cars.

For more information on green cars and to keep up the latest green car developments, visit TheGreenCarWebsite.co.uk.

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