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Reciprocating Detonation Engine

Revision to the Miller Jet
  [vote for,

Reflecting on my recent Miller-jet idea, I knew something must be amiss with the idea for me to have questioned [Vernon]'s two cents.

I got to researching the ideal Carnot Cycle; in which the system's efficiency mainly depends on the heat difference between two reservoirs; lowering the cold input has a much more profound input than raising the hot side. I wonder if this may more closely mimic that.

Imagine you have a 1.4L 3-cylinder TDI engine block lying around from a late model VW Polo; you de-stroke it utilizing the short-stroke 1.0L BlueMotion crankshaft so as to allow longer connecting rods and a larger rod:stroke ratio. In addition, you top it off with the BlueMotion's Aluminum DOHC 4-valve heads, and some 80:1 (yes 80:1!) pistons. Also, we will be using gasoline as the main fuel source and not diesel.

Here's where it gets fun. A cylinder inhales it's full volume of a whopping 333ccs.As soon as the intake valves closes, the exhaust valve opens and remains open for half of the compression stroke. A port fuel injector is placed in the exhaust port, spraying gasoline onto the exhaust valve-stem, and concurrent with exhaust flow. While the piston pushes this half out, the turbulence of the fuel flowing past the valve-stem both cools the valve and provides turbulent mixing of the air/fuel mixture in the exhaust tube.

When the exhaust valve closes, there is still another 40:1 of compression, and half the physical distance remaining before TDC. A dual-fuel direct injector puffs a small amount of high-cetane ignition fuel right into the piston bowl once the piston has completed ~3/4 of its travel to the top; generating a small combustion event. A few degrees later, the exhaust valve re-opens and allows the piston to expel the lean combusting charge out of the cylinder; colliding it with the already present and mixed air/fuel mixture in the tube. This is how Pulse Detonation Engine's work; and a (detonation proof) Disk Turbine may be inserted into the flow of the collective pulses as a way to extract work; a bladed turbine would probably suffer explosive failure.

The high rod/stroke ratio mentioned above means that the piston's velocity will be the greatest during the first 3/4 of travel up to TDC, and will increase dwell time right before and after TDC. This allows us to utilize the extreme 80:1 geometric compression ratio to force out all of the air/fuel charge and products very effectively while leaving the piston in very close proximity to the head. Obviously, using a piston engine as a pulse-compressor, or pressure buildup compressor rather, will generate a huge amount of compression heat that will be sunk into the components of the engine. Fear not; the second fuel used in the dual-purpose direct injector is water!

That's right folks; Bruce Crower himself would be in awe! All of that component melting, piston-seizing, oil-boiling unnecessary heat from a positive displacement compressor/detonation ejection hybrid provided a perfect power stroke by means of flash steam @ TDC; to the tune of a high-torque 80:1 expansion ratio. That 4th, unaccounted for valve is a separate steam exhaust into a low-pressure drop condenser.

acurafan07, Jul 17 2013

Pulse Detonation http://arc.uta.edu/research/pde.htm
[acurafan07, Jul 17 2013]

Anti Turbo-Lag via Delayed Ignition Backfiring http://en.wikipedia...wiki/Antilag_system
[acurafan07, Jul 17 2013]

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       So, in short, like a cross between a Wankel running an inverted cycle, and an overblown Newcomen engine, with a dash of upstroke recycling?   

       Or not?
MaxwellBuchanan, Jul 17 2013

       [Maxwell] What a beautiful question. I'm going to take a shot in the dark and say, maybe? Tis somewhat of a whole new beast.
acurafan07, Jul 17 2013

       Perhaps it is useful to point out that during the first half of the compression cycle, while the exhaust valve is open, the fuel/air mixture will be expelled into the manifold where it will come into contact with hot combustion products from the preceeding cylinder's firing cycle.   

       We conclude that the consequence may be unintended premature ignition, and "blowback", increasing the pressure in the cylinder once the exhaust valve has closed.   

       Please build this engine immediately, and post the video on the web. We take it as read that you favour cremation over interrment.
8th of 7, Jul 17 2013

       [8th], you should really leave the technical critique to those of us who understand it.
MaxwellBuchanan, Jul 17 2013

       [8th] With a stock or log manifold- absolutely. I would create a live video feed straight to you with exclusive rights to its royalties/submission to the popular American TV show '1,000 Ways to Die'.   

       Pulse Detonation Engines do usually use an inert purge gas for just that reason; I'm figuring that with a set of merge collectors, which admittedly I forgot to mention within, there would be enough flow separation so as to more similarly mimic a so-called 'Rotating Detonation Engine' (a type that does not require purging) and ideally prevent the pulse-crowding and crematory backfire you speak of.   

       The Turbine is not envisioned as being in too close proximity to the engine but rather a few feet downstream; as bladeless turbines extract their energy from a gas's velocity rather than its' outright pressure.   

       As an aside, any inventor familiar with Rudolf Diesel's tale of woe should at least have half the mind to test their creations at a safe distance.
acurafan07, Jul 17 2013

       Yeah, that's what I was going to tell them. Spot on.
MaxwellBuchanan, Jul 17 2013

       // which admittedly I forgot to mention within //   

       Oh, NOW he remembers, after it's been pointed out ...   

       What's the temperature of the discharger manifold ?   

       If it's above the auto-ignition point of the fuel air mixture, "WhoooshBOOOM" still applies.   

       If not, it will have to be cooled. Which is a waste of energy ...
8th of 7, Jul 18 2013

       [8th] Another beautiful question if I've ever seen one. Because the power stroke is replaced with a flash-steam stroke removing all heat build-up in the cylinder, the reciprocating enigne/head should sink the heat of compression fairly well.   

       Also, the behavior of the discharger manifold is to receive pumped air while vaporizing gasoline past a valve-stem for half the up-stroke- rather than the entirety of the exhaust stroke being used to shoot out a slow deflagrating mixture against high back-pressure (as in Antilag). For the time that the fuel is being injected and vaporizing, it is absorbing heat and inhibiting pre-ignition (hopefully).   

       But, I do know that Propane has an Octane rating somewhat higher than gasoline of ~100. Propane is also mentioned pretty frequently for proposed PDE fuel while gasoline is not; perhaps we want to use it in the tubes instead of gasoline to prevent pre-ignition. Even so, I wouldn't imagine the intermitant pulses would be cause for a lot of heat sinking.   

       When we close the exhaust valve for a bit to build up some compression within the cylinder for the detonation ejection aspect, the charge in the discharging manifold may have absorbed enough heat to ignite; probably not. Either way, it does not matter by now; when the exhaust valve re-opens to expel the detonation event, it doesn't matter what's going on in the tube since the positive displacement piston is going to force out its entire volume regardless (decreasing volume deflagration > tube deflagration).
acurafan07, Jul 18 2013

       Does anyone else think this will work or not work?
acurafan07, Jul 20 2013

       I, for one, am confident that it will indeed work or not work.
MaxwellBuchanan, Jul 20 2013


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