DISC, for Direct-Injection Stratified Charge, evolved in the late 1980s. Two low-pressure injectors were sited on either side of the rotor chamber close to the trailing spark plug. High-speeed air injected in the nozzles' sockets aided fuel atomization. Engine speed was controlled by fuel injection, which reduced pumping losses by the absence of a throttle. The engine also required less cooling as combustion took place in a more localized area, which also reduced emissions of unburned fuel (hydrocarbons). But the lower exhaust temperature caused another problem: It wouldn't light up the catalytic converter!
DISC-II solves that problem with an elaborate fuel/air management system. It involves a pilot injector and spark plug in a small subchamber peripheral to the main chamber. The pilot injector sprays through the subchamber to the main chamber, formnig a pocket of rich mixture in the main chamber. This pocket is ignited by a flame front from the stable mixture in the subchamber. Meanwhile, the main injector shoots fuel into the main chamber past a conventionally (for a rotary) located spark plug.
And while Mazda put Miller-cycle technology into a production piston engein in the 1995 Mazda Millenia in the spring of 1994, it was also working with the pumping-loss philosophy with the rotary engine. "Pumping loss" is the energy an engine wastes at closed or small throttle operation, when trying to draw in air. The Miller-cycle rotary, called "near-future" in Mazda press material, allows a great volume of air to be supplied to the rotor chamber. Any excess of air is released via a "late" side port controlled by a "pumping-loss control valve" which recirculates the excess air to the intake port behind the throttle. Direct fuel injection solves the problem of mixture control with a single injector later than the "exit port."
My comments:
Direct injection would appear to solve a number of the rotary's problems. For one, while the rotary has superior mechanical efficency to a piston engine, it has poor thermal efficiency. This fault reduces the potential power and efficiency of the engine. Second, the rotary engine is inefficient with fuel and has poor emissions. Direct injection produces more precise measuring and allows for stratafied charges (gas clouds of varying density of fuel) to improve fuel efficiency and ensure more complete combustion occurs, meaning improved emissions. The problem mentioned with respect to DISC-I is that the catalytic converter did not receive enough heat. I have trouble believing that the thermally inefficent rotary with direct injection cannot produce enough heat for a modern catalytic converter, but a 1L 3-cyl engine can. My point is that I imagine that this problem is now more or less solved.
DISC-II seems overly complicated and probably no longer necessarly. One point of interest is that the rotors used in the DISC-II engine are of the trailing recess variety. Leading recess rotors have a deeper dish towards the front of the direction of rotor travel, which I believe were found in some FB rotors. The DISC-II rotors remind me of the Curtis Wright rotors that triangular shaped tips with that extended out to create a deeper dish. Picture adding a triangle over a rotor tip from the side profile, with the edges protruding out, it looks almost like an arrow head. The DISC-II rotors have this arrow head profile on at the front of the flame front, but at the back it actually does the opposite and atttachs ot the tip tip of the rotor at a sharper angle.
I really like the concept of the Miller Cycle engine and I do not understand why more of these engines have not been produced. Essentially all Miller Cycle engines are supercharged, which to me seems more efficient than being naturally aspirated. Second the engine's efficiency is improved meaning more fuel economy and potentially more power. The rotary engine needs all the fuel economy improvements it can get. Rotaries are typically lacking in low-end power, so a supercharger would improve that situation. In piston direct injection forced induction engines they are able to run high compression ratios in boosted applications, without causing detonation. Presumably this trait would be true in a rotary, meaning that power and efficiency could occur at the same time. Mazda has produced a direct injection engine for the Mazdaspeed 6 and some JDM vechiles. I think that the rotary despirately needs some improvement to keep pace with modern piston engines and these solutions seem ideal.
My understanding is that N/A direct injection engines can run a higher CR than simple port injection engines. My understanding of the current geometery rotary engines is that they cannot run a CR above 10.5:1. I do not know for sure, but it would be terrific if they could run higher CRs with rotaries. As it is, the RX-8's Renesis has a 10:1 CR engine making 215-220hp on premium fuel. Other engines such as Honda's 3.0L V6 are able to make more power with the same or higher CR on 87 octane gas. Considering there is only a 0.4L displacement difference and the Accord engine makes 20-25hp more, I consider the Renesis lacking.
If you have any thoughts, knowledge or further info on any of the above, please PM me (Snrub) on the RX-7 forum, I love to discuss it with you.