Burn More Of Your Fuel
 

If our cars and trucks, whether old or new had a cleaner burn in the combustion chamber, catalytic converters wouldn't be needed, would they? Isn't that what the catalytic converter is designed to do? Burn/oxidize the fuel/exhaust that was not completely combusted? It's obvious by looking at the black carbon build up on the end of practically all exhaust pipes (even new cars and trucks) that engines do not burn all of the fuel. The problem has never been about the fuel that the engine burns, it is the fuel that your engine doesn't burn. Incomplete combustion.

MPG will increase when you burn more of your fuel.

You have a point, but if you look at the emissions from a car 20 years ago, and compare it to a similar sized car from today, you'll see today's cars are up to 50% more efficient, if not more. Strict emission standards are forcing manufactures to develop new clean technology all the time, electronic controlled tappets/fuel injection, cylinder deactivation, stop/start technology etc etc. It's near impossible to burn 100% of fuel, but cars and trucks are getting greener every day!

Thermal efficiency is the key to what you're saying. Putting more of the energy burned down to the road as work performed is what will be concentrated on. As far as actually burning more of the fuel, direct injection is probably the best tech going forward. High pressure fuel gets broken into smaller droplets, evaporates more easily into the air, and this is burned more effectively.

Other ideas such as pre-heating the fuel or ionizing the charge have proven more unicorn than practical or effective.

Catalytic converters are charged with oxidizing unburned fuel, but are also responsible for minimizing other pollutants.

Yep, JCP385 is right on the money. Basically 100% of the fuel is already burned during combustion, on modern engines, once the car is warmed up. Older engines (especially high performance engines from decades past) this was not the case. Converting the heat energy from combustion into useful work ("thermal efficiency") is where the vast majority of energy waste occurs.

Soot is a natural byproduct of combustion (much more so for diesel than gasoline) and that is why we will always have it all over the tailpipe.

And its not uncommon on tuned turbocharged cars for them to over fuel, and you get awesome explosions as the unburnt fuel ignites in the exhaust. This is my old car backfiring.

Fiat 500 Abarth - Exhaust backfires! - YouTube

Soot is unburned fuel in the form of carbon particles. In gasoline engines soot deposits are usually seen as a sign of running rich.

All piston engines waste a small percentage of fuel, on the order of 1% to 3%, because some of the fuel mixture is compressed into the space between the piston and cylinder wall and the space above the compression ring. These spaces are quite small, so the mixture in them is cooled by the surrounding metal and will not burn. As pressures drop during the power stroke some of the mixture comes out and is burned, but never quite all of it. Carbon monoxide is incompletely burned fuel. The job of the catalytic converter is to finish burning the unburned fuel, sometimes with the aid of air injected into the exhaust system after the exhaust valves.

All good related points, but dodging around a major problem. The EPA & "ethanol in gasoline industry" say, adding 10% ethanol to fuel only decreases mpg by 3%, by its lack of btus. When "ethanol in gasoline industry" wants to ramp up its lies, they say 1.5%. Any easy driver that is patient & carefully monitors their mpg for a continuous year of 10% ethanol blend(E10) AND a continuous year of 100% (ethanol-free) gasoline(E0), will show E0 increases mpg by 8%, 7% & 5% over E10, as I have for three 87 octane gasoline designed cars. Yes, only adding 10% ethanol to fuel collapses mpg by 8%, 7% & 5%. It is obvious that ethanol as used(not burned efficiently) in low compression ratio(9:1 to 12:1) gasoline engines, needs high compression ratio(16:1) ethanol engines to extract the energy of ethanol efficiently. 87 octane E0 has gas molecules averaging 87 octane(duh)! However, 87 octane 10% ethanol blends(E10), first has 114 octane ethanol added to it. For 87 octane 10% ethanol blend to average 87 octane..... now listen up.....the gasoline molecules must average 84 octane. Not only is the 114 octane ethanol way out of the design parameters for an 87 octane gasoline engine, the 84 octane gasoline molecules are ALSO, outside the parameter design for 87 octane gasoline engines. Its a wonder that E10 loses only 8%, 7% & 5% mpg.

None of this is difficult to understand. 87 octane gasoline engine engineers are good & have designed low compression ratio (9:1 to 12:1) gasoline engines to burn 87 octane E0 well. Also, 114 octane ethanol engine engineers are also good, designing ethanol engines to burn ethanol efficiently. However, ethanol does NOT process properly in gasoline engines.