As much as 3 years ago there was a thread also started by RED about a 6000 RPM Diesel engine citing the same Pattakon engine, to which I posted a reply. I think much of the discussion there is relevant in this thread, so here is the link:
http://forums.tdiclub.com/showthread.php?t=66597
The important point that was mentioned but obviously overlooked was the ignorance of the important distinction of combustion processes occurring in the time- and crank-angle -- or analogously, the frequency -- domains … someone either never took or failed a course in Laplace transforms
… for that reason, I quote it again below for emphasis:
Heywood and others have found that in contrast to conventional gasoline engines where the rate of combustion scales according to crank angle, in Diesel engines, combustion proceeds largely as a function in the time domain.
What this basically means is that in a gasser, combustion begins and goes to substantial completion in a relatively constant number of crank angle degrees whether at 2000 rpm or 6000 rpm, although at 6000 rpm there's 1/3 the amount of time in seconds for this to happen.
In contrast, in Diesel engines, there is a {rate-limiting, time-dominant} component of the fuel injection, mixing and ignition delay within the overall combustion process that takes a relatively long, fixed and finite amount of time in seconds, largely independent of crank angle. So, as the RPMs rise, these processes must occur over a greater number of crank angle degrees for a given amount of time, or what we know as "dwell."
What this means in plain old English is that even if the “constant-volume” dwell in crank-angle degrees can be increased by some novel engine mechanism design, you will not get a proportional increase in revving capability of a Diesel engine.
Premixed (read gasser) combustion appears to scale with RPM due to small-scale turbulence also exhibiting this RPM (actually mean piston speed)-related behaviour (ref. Heywood). Diffusion (read Diesel) combustion is limited to the rate of diffusion, which means the physical, state-change process of fuel jet molecules evaporating and entraining into the hot compressed air and forming locales of combustible fuel-air mixture (ref. Peters, Heywood, etc.). This is only (relatively) weakly affected by turbulence due to the enhanced transport of fuel molecules in a turbulent flow-field vis-à-vis laminar or quiescent ones; and the enhanced convective heat transfer and therefore liquid fuel evaporation rate.
That said, many non-conventional engine mechanisms have been devised over the years in order to maximize this dwell at TDC, so that said, this concept is not new.
For that reason, despite being flammed for my oversight, I have lumped all engines with these kinds of mechanisms as simply variations of the scotch-yoke, not because they are design-similar, but because of what they all try to achieve geometrically in terms of the cylinder-volume-to-crank-angle relationship.
It should be pointed out that the benefits of a long dwell at TDC does not only benefit Diesel engines but ALL engines that work on a thermodynamic cycle. This is because for a given compression ratio, thermal efficiency increases as you go from a constant pressure combustion process (not really achieved in modern engines) to a constant volume one (also not really achieved in the real-world); both spark ignition and high-speed Diesel engines work on a process that is approximated analytically by a thermodynamic model that is something of a hybrid of the Otto (constant volume) and Diesel (constant pressure) cycles. This is known as a "pressure-limited" or "dual-combustion" cycle.
Unfortunately, this is a highly idealized, Thermodynamics 101 analysis of engine cycles. While true in the idealized sense, it does not take into any account the real-world realities of engine design, such as non-quasi-stationary workings of an engine, as well as practical limits of peak cycle pressure (due to engine structural strength) and peak cycle temperature (due to the realms of possibility of combustion rate and temperature of common fuels; thermal stress and NOx emission considerations).
In “Thermodynamics 201,” one has to apply knowledge from many other disciplines (mechanics, design, combustion, chemistry, etc.). All real-world engines have to consider limiting values for peak cycle pressure and temperature, and with these in mind, the best compromise for high thermal efficiency, high BMEP, low engine stresses and low NOx emissions is NOT a pure constant-volume cycle but rather something in between a constant-volume and constant-pressure one. In fact,
one can find by calculation, that with a given limiting maximum cycle pressure, the highest thermal efficiency is actually achieved with a pure constant-pressure cycle! This can also be illustrated qualitatively and graphically by sketching a T-S diagram comparing the different cycles of interest to a Carnot cycle operating within the same temperature and pressure limits, and any mechanical engineer worth his salt is called upon to be able to do this task!
To summarize, it is sound theory that by lengthening the dwell at TDC, a Diesel engine can be made to rev higher, within the boundaries of other geometrical considerations and limitations in the combustion process.
Still a true statement, but I just want to point-out and emphasize an X% increase in TDC dwell will not mean an X% increase of RPM capability, nor an X% increase in HP potential, nor an X% increase in efficiency,
