New technology to increase the fuel efficiency of fossil fuelled vehicles is coming onto the market all the time. The idea is to either tinker with the engine so one can produce a less thirsty engine or reduce the drag coefficient of the vehicle (making the vehicle body more aerodynamic so it slips through the air with less resistance). This is the approach of the car manufacturers to the new EU legislation which requires all car manufacturers to have an average emission from their range of vehicles of 130g CO2 / km or less (130 grams of carbon dioxide emitted per kilometre or less). There are many technologies already on the market as part of new cars but there are some more subtle technologies seeking to push the economy to the limit.
Already Present
Some excellent examples of this new and emergy branch of automotive engineering are the aerodynamic enhancements made by Ford to their new breed of vehicles. http://media.ford.com/article_display.cfm?article_id=34312 This article shows how the designers and engineers put their cars in the wind tunnel and test for drag and they work to minimise this. An excellent product of this process is the active shutting grille. At high speeds, motors at the front of the car shut the grille fins forming an air dam. This minimises air drag off the front of the car and this kind of technology is used all the time by hypermilers wishing to increase fuel economy by crazy amounts: http://ecomodder.com/forum/showthread.php/effects-air-dam-ford-f350-pickup-3171.html
Another passive technology is the sculpting of the bodywork of the new vehicles to reduce disrupted airflow over the vehicle: http://www.volkswagen.co.uk/#/new/car-range
Start, stop, restart
A technology usually reserved for the higher end luxury models is the start-stop technology which involves an on board computer shutting down the engine when the car comes to a stop then starting it up again when the accelerator pedal is depressed when the lights change. This saves fuel by simply turning the engine off and this technique can be utilised by every vehicle when a lengthy stop at the traffic lights is on the cards.
A look to the future
New exhaust technology being pioneered at the Universities of Cardiff and Birmingham intends to further increase the fuel economy of vehicles by injecting fuel into a conversion unit in the exhaust, allowing it to react using the heat of the exhaust gases and then passing it through the engine. This is a more efficient way to use fuel as it converts simple diesel or petrol into carbon monoxide and molecular hydrogen which are better fuels than simple hydrocarbons. It is a 'green' approach too as it utilises the waste heat of the engine to drive the chemical reaction of conversion of the fuel. The average gains from preliminary testing are suggested to be around an extra 10% mileage with diesel engines and 20% with petrol engines. The lead scientist for this process, Stan Golunski, has been working on the concept for more than 10 years and expects the techology to be perfected and on the road before 2020. http://www.theengineer.co.uk/news/on-board-fuel-reforming-could-enhance-vehicle-efficiency/1005487.article
