IC engines consume most of our oil. Majority is used for moving people-passenger cars the worst. To reduce the oil produced the entire system needs to be optimized. A car, for example, uses about as much energy making it as it burns over its life of 150 thousand miles or so. Substituting a diesel engine for a gasoline engine will use more fuel for a given passenger vehicle. Much of improved mpg comes from the fact that diesel fuel packs more energy per gallon. The rest derives from the fact that the diesel version will be slower. Unfortunately, added energy is needed to make the diesel engine. Amount of total energy used is the parameter of actual interest. This fact is usually considered too complicated to bother with.
High IC efficiency is well understood: Burn fuel fast as lean as possible at optimum compression ratio (CR). There is an optimum CR. Increasing it betters thermal efficiency at the expense of mechanical efficiency: Total is best at optimum CR. Optimum increases with rpm.
The variable compression ratio and charge (VCRC) engine increases both % air and CR as torque demand decreases: CR stays optimum. This raises thermal efficiency to compensate for reduced mechanical effectiveness as torque decreases. The engine does so by combining all the vaporized fuel and some of the air in a variable volume where initial combustion occurs. Exhaust products then mix with rest of the air to complete a lean burning. Initial burn volume is cycled between zero and operating value each cycle at low engine pressure to ensure both adequate lubrication and low friction.
Efficiency of pollution is maximized. Initial combustion occurs in uniformly mixed over-rich blend. Burn in such is both fast enough and produces vanishingly small oxides of nitrogen (NOX). Combining hot exhaust products with excess air takes care of unburned hydrocarbons and carbon monoxide (CO).
Automobiles operate at very low average power. VCRC efficiency is at a maximum at 20-40% of peak torque. Its average efficiency is twice that of a gasoline engine...it is also less than half the weight of that typical power plant. Thermal efficiency at idle is 20-40%. It is also light. Its two-stroke configuration combined with insensitivity to octane means about 3 HP/pound is possible.
In conjunction with its fuel tolerance-tested with 50/50 gasoline/diesel oil-it can deliver three times the fuel mileage per oil barrel: Tolerance for low octane or cetane number is nearly unlimited. 54.5 mpg fleet average is readily attainable with it.
Its system weigh reduction is manifold. VCRC is light enough to mount aft of rear axle minimizing both system layout weight as well as easing wheel size requirement. Its maximum efficiency at low torque means fewer transmission speeds needed. This latter characteristic improves drivability as well.