Why Is 100% Efficiency Impossible on Anything?

Car's engineIn an ideal world, cars are 100% efficient. Fuel never goes to waste, and the amount of energy output is equal to the amount put into it. But alas, this is not an ideal world. Modern car engines, despite advances in engineering and design, can only manage 25-30% efficiency. Experts have also said that 100% efficiency is theoretically and practically impossible.

It’s understandable that any drop in these measly readings is enough reason to visit a local car mechanic, in shops such as LRC Automotive. Every litre of fuel counts in light of constant oil price hikes. As for the hope of building a 100% efficient engine, there’s enough scientific proof of its impossibility.

Thermodynamic Laws at Work

Much of this has to do with the First Law of Thermodynamics. Keep in mind that a car engine is a heat engine. According to the First Law, the total amount of energy in an isolated system is conserved. This involves the three major component of a heat engine: the hot reservoir or heat source, the cold object/heat sink, and the object on which work is done.

Work is only present when there’s heat transfer. This occurs when heat flows from the source to the heat sink. Heat sink and source temperatures equalise as heat is transferred. When temperatures are similar, there’s no heat transfer going on. The lack of temperature difference means that no heat can be converted to work. Unless there’s temperature equalisation, heat will continuously be produced until it has to be expelled. Therefore, it goes to waste — and so does 100% efficiency.

When Things Come Close Enough

Cars can’t really come close to 100% efficiency, but theoretical spacecraft probably can. NASA is still toying with the possibility of antimatter propulsion systems. Featuring ordinary matter particles with opposite charges (mirror images of conventional matter in the universe), antimatter’s energy density is crazy. Up to 40% of its mass can be converted directly into thrust. Nuclear fusion is at a measly 1%. 10 thousandths of a gram’s worth of antimatter has enough power to send a ship to Mars in 45 days. Conventional rocket-powered spacecraft cover the distance in 7 months.

Still, antimatter is not 100% efficient. It incomprehensible amounts of energy to produce microscopic amounts of antimatter, with the samples barely having enough power to propel ships anytime soon. It seems like the 100% efficient engine will stay mythical.