The internal enchantment engine is a spell device created in LY 911 by a team of Sorreters led by Cirna Mastera. However, unlike most spell devices, the IEE is actually more mechanical in nature than magical. It was inspired by the invention of piston pumps over two decades earlier, by Lyle Miller (though pistons had been used in mills for several centuries prior to that). It is known that on Earth there is a more complex type of machine called an "internal combustion engine," which is powered by burning fossil fuels, which have yet to be discovered on The Land. (Such engines may be powered by other fuels which do exist on the Land, such as ethanol or plant-derived oils like that of threenuts or oddberries, though it would be less efficient.)
However, the IEE is powered by a spell designed to produce reciprocating motion in pistons, which are attached to a crankshaft. The crankshaft converts the reciprocating motion of the pistons into rotation. It is connected to the wheels of the vehicle (a wagon, carriage, or stagecoach), and the wheels are rotated by the crankshaft, giving the vehicle forward (or when so desired, reverse) motion. As they move, the wheels themselves provide a certain degree of rotational energy to the crankshaft, which then translates it into reciprocating motion in the pistons, thus restarting the cycle. This reduces the amount of work the pistons must do to keep the vehicle moving, as compared to starting it in motion; though some work is still required on their part to maintain a steady speed, particularly on uphill roads or rough terrain. The engine's enchantment is also necessary to increase or decrease speed, to change direction, and to stop the vehicle.
It should be noted that while flying requires two separate spells, one for levitation and one for locomotion, which must be precisely balanced to preserve the structural integrity of a vehicle. These two spells must always be used simultaneously, which means that a vehicle which has been enchanted to fly cannot use just one spell to move over land; it can only travel in the air, at least using magic. To travel over land, both spells must be deactivated, and the vehicle can then be drawn by striders or oxen. A similar problem exists with vehicles powered by an internal enchantment engine. At least in the current model, the spell used to power and control the pistons cannot coexist with the type of locomotion spell used for flight. Nor can it be used in lieu of such a spell, in combination with a levitation spell, simply because in the air there would be no friction on the wheels to produce forward movement. While the team that developed the IEE spell continue to experiment, for the time being any vehicle powered by such an engine can only travel on land.
IEE-powered vehicles, however, can reach speeds of 60 mph or more. While not as fast as flying spells (which may reach 80 mph or more), it is still faster than a team of striders, which typically can go up to 40 mph. (This is top speed, and can't be sustained for long; a more common speed for striders is 10-15 mph, or at best upwards of 25.) Of course, there is also no need with IEE to stop periodically, as one would have to do to let their striders or oxen rest. The IEE also eliminates the need for feeding and housing draft animals, as well as the unpleasant task of mucking out stables. It also requires recharging far less often than the magic which powers flying vehicles, since it only uses one spell instead of two, and because only the engine itself is enchanted (as compared to the whole vehicle with flying spells), and because of the slight recycling of energy provided by the locomotion itself. So, unless you absolutely have to fly, IEE-vehicles are quickly becoming the preferred method of travel, due to greater convenience and cost-effectiveness.