> insulation or one of the various waste-heat-recovery systems that transfer some amount of the heat remaing in outgoing exhaust gases into incoming working fluids?
Several reasons this isn't done in the engine intake. The main power conversion in a ICE is through the thermal expansion of the gasses trapped in the cylinder, so heating it before the intake valve is closed only reduces the density of the air taken into the cylinder (PV=nRT so at the same Pressure and volume, the higher the temperature, the fewer molecules, less O2 available to burn.) Once the air is trapped in the cylinder all heat added will then be converted, so a cold intake, then a hot block helps contribute to efficiency. But then metals have limitations on the allowable temperatures (for at least the last 40 years Ceramic engines have been on the verge of a breakthrough making higher temp more efficient engines a reality, maybe next year.) Also combustion properties of carbon fuels create emissions problems when combustion occurs at too high of temperatures.
Power stations will harness the waste heat from Ng Generators, and pump that into a sterling engine, then take that waste heat into another conversion, then take that waste heat as warm water for buildings, etc. But that takes too much space, weight, and cost (I assume) to be put into a mobile vehicle (other than used as a heater in the winter.) Although I would hope Cruise ships, etc would utilize this waste heat as well.