Pull up your modern sedan alongside a Model T Ford and the two will hardly seem related. Yes, there are still four wheels and a steering wheel, but that is where similarities seem to end.
Modern cars, are large, sleek and aerodynamic; made of advanced lightweight materials and feature a host of safety features. The Model T by comparison had no seat belts, air bags or anti-lock brakes, sat high off the ground and was made of steel, wood and even horse hair.
But open the bonnet – or hood, if you prefer – and there is a strange anachronism. The engines of both cars will likely still consist of very similar technology with four pistons moving up and down in four cylinders.
And what is more, the fuel efficiency of those engines has hardly altered. That first mass-produced car had an inline four cylinder engine, which produced 20hp (15kw) with a claimed fuel economy of 13-21 miles per gallon (mpg). Your sedan will likely have a modern four-cylinder engine that likely produces more like 200hp, but only with a slightly improved fuel economy of somewhere in the range of 20-30mpg.
But all that could soon change. The United States has just announced new regulations, which will require car makers to produce vehicles which go further, on less fuel. “We’ve set an aggressive target and the companies are stepping up to the plate,” said President Obama in a statement. “By 2025, the average fuel economy of their vehicles will nearly double to almost 55 miles per gallon.”
Of course, in European countries where smaller cars and diesel engines are commonplace, these kinds of targets don’t seem that aggressive. But for the US, where emission laws prevent some of the technologies already used elsewhere being used, they are ambitious. And, what is more, they are likely to spur a new era of engine design that will not only replace the old fashioned four stroke, but could also change how engines work in the US and elsewhere.
Almost all engines today work on the principle that if you put a small amount of fuel, like petrol, in a small, enclosed space and ignite it, it explodes with a huge amount of energy. This can then harnessed, via a connecting rod and crankshaft, to drive the wheels.
Most engines do this several times a second using what is known as the four-stroke cycle. In this, an engines pistons rise and fall within its cylinder four times – known as the intake, compression, power, and exhaust strokes. In a modern, direct-fuel injected engine air is drawn in as the piston falls in the cylinder, then compressed as the piston pushes back up. Almost immediately fuel is injected and ignited, forcing the piston back down again in what is known as the power stroke. The final stroke of the piston expels the combustion products.
To ensure that there is continuous power, most cars have a series of cylinders – commonly four – allowing the pistons to be at different points in the cycle. Six or eight cylinder engines work on the same principle. Between them, these engines power almost all cars, boats, trucks, propeller aircraft, generators, and so on.
There are variants of these designs, which could help the US meet its targets. For example, hybrid vehicles which use a combination of electric motors and petrol engines already achieve fuel efficiency of close to 50mpg. In addition, manufacturers like Ford and Fiat, have introduced engines with fewer cylinders from the usual minimum of four; three in the case of Ford and two for Fiat. Both use turbochargers and clever timing-control to burn less fuel whilst maintaining the same power as other engines. Ford’s engines will be introduced to US cars next year.