Can Non-Hybrid Cars Get 100+ MPG Today?
We're not talking about hybrids here; our topic is cars powered by the basic IC-engine that relies on gasoline and not electric motors. Today's gasoline engines are not designed to combust/burn gasoline efficiently. Even with the advent of using high pressure fuel injection techniques that are computer controlled, we still fall short of the mark. Partly because liquid gasoline can't burn, only gasoline vapors burn, and there lies our problem. The same goes for injecting the high pressure droplets of fine-mist liquid gasoline that enters the engine cylinder using our current nozzle ejector technology, it doesn't all burn at the same time!
Engine designers assume that these droplets are instantly vaporized by the engine's hot cylinder walls, and then instantly explode/combust when ignited by the sparkplug. Not true, up to 2/3 of the fuel isn't vaporized and doesn't combust until later on in the cycle. The 1/3 that gets almost-instantly vaporized and burns will do so within the several thousandths of a second (Fig-1) it has before the piston moves down its 1/2-stroke (out of today's 4-stroke cycle) completing the engine power-portion of its cycle. This releases power and tremendous heat which indeed vaporizes the remaining ~2/3 of our fuel from its liquid droplet form, but too late. It essentially does so when the power stroke is almost over or the piston is just about ready to move into its up-stroke (2nd stroke of our four stroke cycle) phase. So, because of poor vapo-timing we have 2/3 of our fuel virtually wasted by exploding at near the bottom of the power stroke.
This incorrect explosive timing, which happens to most of our fuel, imparts very little energy into the crankshaft because its effective "moment" (a product of explosive force and radial-component distance from crankshaft center) is insignificant by then. Various attempts at adjusting the combustion timing spark hasn't made a significant difference. Even though ~2/3 of the fuel is now exploding and providing a huge force, its small "influence" arm distance is rapidly diminishing to zero, and any huge downward force times near zero arm-length is still zero.
Some clarification here, technically thermal-efficiency is not improved, pretty much all of the gasoline gets combusted today. That means the energy of the fuel is almost totally released, but not effectively used. The problem is the timing it takes to convert fuel-injected gasoline droplets into vapor to combust at the correct engine rotational time and extract that expended energy. If you did the math for any size engine rotating at say 3200 RPM, you would find that a 4-stroke engine can only extract that energy from combustion during one of the four strokes. And the time it takes to make that stroke happen is only about 9.4 thousandths of a second or 9.4 milisecs (msecs).
Now picture the piston just below TDC, all its valves closed, under pressure and containing all the fuel and air it needs to combust. At this point our deadly cocktail has about half of the 9.4 or about 5 msecs to complete combust after the timed sparkplug ignites it. The half factor exists because the max portion of our power stroke (moment arm) occurs at the mid-stroke of the piston sliding down and turning the crankshaft. If all of our fuel isn't combusted by then, the moment-arm or distance from the piston-center to the crankshaft quickly reduces to zero. Again, only vapors combust within a healthy 2 msecs (Fig-1), while fuel droplets take a relatively long time (>5 msecs) to vaporize before it can combust. Unfortunately nature is stubborn and vaporizes ~2/3 of our injected fuel droplets only during roughly the second half of the power stroke. So this huge amount of energy gets wasted because even though the forces of combustion are huge, its moment arm is rapidly approaching zero. Infinity times zero is still zero!
Engine designers/engineers have been plagued by this phenomenon ever since the creation of the 4-stroke gasoline or Otto cycle engine. We need to improve this intermittent combustion/explosion process by combusting all of our injected fuel at the correct timing sequence. This is accomplished by injecting only vaporous fuel which will produce ~3X the power we now get. Another way to state this is, for the same power that we now get from a gasoline engine, if we burned the fuel correctly, we would only need 1/3 the fuel consumption to get 3X the current MPG.