For about ten years, solutions have emerged to replace diesel or gasoline cars, considered too polluting. But to date, no alternative fully meets the requirements of this means of transport. The electric car is criticized for offering too little autonomy. Biofuels have a poor energy balance. And cars running on hydrogen, its exorbitant costs. So what fuel to offer performance, autonomy and respect for the environment?
Newsletter Science&Vie
Receive all science news, three times a week
—-
Metals could meet these criteria. Among them, magnesium is one of the most abundant in the earth’s crust. In powder form, it is an easy to transport and above all renewable fuel: the metal oxides produced during combustion can be recycled. “This is the great advantage compared to hydrogen and biofuels”, underlines the doctor engineer-engine engineer Driss Laraqui, whose work relates to the development of this technology.
>> Read also: What is the ecological balance of an electric car?
How does an engine powered by magnesium work?
The magnesium powder, gray before combustion, is finer than sand and obtained by grinding the metal. Unlike gasoline, it requires an engine whose combustion chamber is outside the piston chamber, to avoid clogging the cylinder with the particles produced. This particular engine is called Stirling (named after its inventor).
The principle is simple: the combustion chamber encloses the magnesium flame so that it does not move, in order to recover the radiation. This combustion heats an inert gas in the piston chamber, which is not directly in contact with the flame (unlike internal combustion engines). Under the effect of heat, the gas expands and actuates an intermediate piston which moves in the cylinder, which in turn actuates the motor piston. This heat engine operates continuously to recharge the battery, itself emptied by the electric motor which drives the wheels. It is therefore a hybrid engine: both thermal (which recharges the battery) and electric (which drives the vehicle forward).
During combustion, the oxides (metal waste) produced are recovered using a filtration system. These will be recycled in a fixed station powered by solar panels: the MgO oxide molecules are broken to obtain magnesium on one side, and oxygen (which escapes into the gas on the other). ‘air). The powder is therefore almost entirely recyclable. “If the yield is 99%, the same mass can be renewed 100 times. If the efficiency is 90%, it will be 10 times ”, specifies the engineer.
The fuel can therefore be recycled a number of times before having to extract magnesium from the ground to supplement it.
