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The
principle of the recuperative engine, tradenamed Hx™ or "wix",
is that the exhaust is passed through a recuperator (aka a heat
exchanger) at the instant it leaves the cylinder. Over half of
the exhaust heat transfers to the recuperator, resulting in the
exhaust being released much cooler than in an Otto engine and
improving theoretical Carnot efficiency. A couple of milliseconds
later, the captured heat is transferred to a compressed air charge
entering the cylinder. Thus half of the heat normally wasted in
an Otto is used in a Hx engine to superheat the next charge. This
heat transfer is accomplished almost for free. Direct fuel injection
into the cylinder is then used in lieu of normal port injection
or carburetion. The superheated air charge is able to ignite a
much wider range of fuel-to-air ratios than will burn in an Otto
engine, allowing partial throttle to be obtained by leaning the
fuel input rather than by wasteful induction throttling as is
required in an Otto engine.
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