American writer Mark Twain once said "It ain't what you don't know that gets you in trouble.
It's what you know for sure that just ain't so." This is especially so in the case of what even well-educated engineers know about how IC engines work. Often what they know is based on an “idealized” p-V diagrams, like the one shown here from
US's NASA. While useful as a teaching aid on the function of the IC engines, the standard p-V diagram is a
“fundamentally incorrect oversimplification”. However, critically examining this theoretical ideal can give us three important clues about how to vastly improve the IC engine concept.
1. This Ideal depiction of how an IC engine works shows the combustion process as a
“constant volume process”. But this would require the piston to stop close to TDC instantly so the volume could remain "constant" while the flame front has time to move through the combustion chamber. Combustion in an IC engine takes place in a
thin interface between the expanding flame kernel and the yet-to-be-burned A/F charge. To instantly stop a rapidly moving piston would cause it to collide with
Newton's laws of motion and would cause lots of things to break.
It just ain’t so that combustion is or can be a constant volume process. In a crank engine, its pistons change direction so fast at the top of the stroke that at high speed they experience from
3500 to 4,000 g-forces. This may cause the piston to retreat faster than the turbulent flame front as shown in image 2. At some speeds the piston is being pushed more by the acoustic shock wave which moves at the speed of sound than by the slowly increasing pressure.
If the piston approaches and departs the top of the stroke at a constant acceleration dynamic this would permit combustion to start earlier and give the flame front more time to move through a smaller space. Such a dynamic gives more time for the heat of combustion to be transformed into work. This also allows more of the combustion event's heat energy to be converted into work, resulting in greater efficiency. Professor Oppenheim also suggested using a different method of combustion
HCCI. More on that later.