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#136
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I am imagining that with a higher flowing prechamber, a larger volume of air will be able to flow into the prechamber, and given that the burn tube would be the stock diameter, the velocity of the incoming air would be grater than as with the stock design. As a result of the higher velocity, the air would be pushed straight up to the injector, scavenging the top, (injector), and then being forced down the sides of the prechamber back to the bottom where the flow would collide into its self and stir up the middle. Spinning it vertically would add some additional swirl and the helix might possibly create some back pressure during the higher injection quantities. Given that the OEM material is very good, I am going to modify the stock prechamber to increase flow and possibly increase the prechamber volume. I am sure that the increased velocity will allow the ball to do a better job than it does in the stock prechamber. Quote:
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#137
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Also, it would be thinning out metal at the very worst place.
__________________
84 300D, 82 Volvo 244Gl Diesel |
#138
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I only need to cut a radius to make clearance for the corner of the tip that is not on the flat end of the original prechamber. The piston has a pocket but it is flat because the end of the prechamber is flat. I will just be adding an angled and radiused relief pocket with the deepest point at the corner, about .150 inches deep. There is plenty of meat there. I have seen both original and up-rated pistons and the only difference is the up-rated piston has a much larger pocket than I am going to be cutting. The bottoms of the piston domes are identical to each other. With the modified prechambers, the cylinder compression pressures, (pre-injection), should be lower, and the compressed, (cylinder), air temperature should be lower as well because more air will be going into the prechamber, making the cylinder and chamber pressures as balanced as possible. The stock prechambers restrict the flow of air into and out of the prechambers so much, that even at idle speed piston velocities the compression pressure is 150% higher in the cylinder than the pressure in the prechamber. It gets worse as the engine speed increases. The excessive cylinder compression pressures create higher temperatures that unnecessarily pre-heat the piston and head, (wasted pumping energy). Additionally my goal is to have as much of the combustion take place in the prechamber it self, before TDC, (a shorter injection pulse width is needed in order to be able to do this at increased delivery quantities). This will allow as much of the combustion heat to be used for work and greatly reduce any residual fuel burning during the power and exhaust strokes with generates unproductive heat and smoke. From the crude testing I have done, I can see that there is opportunity to, reduce/trade, the stresses on the engine from unproductive pressures and temperatures, while/for, increased productive power. But to what degree if any is unknown. Ultimately you are correct in you concerns. I am playing engineer here and that has been known to get people, (myself included), into trouble from time to time. I feel confident in this case, but as I like to say, there is one way to find out. I have made sever thousand dollars of scrap in a mater of seconds on the dyno, I am hoping to avoid that here. All in all these engines are really over kill engineered. It is like they were intended for aircraft use, or something military. As always, I welcome any constructive questions, thoughts and or concerns relating to this thread. |
#139
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I was actually suprized when after getting a Mercedes I saw the crossection pics of the Prechamber in the manual.
I could not believe what would have to be squeezed through the little holes in the prechamber and I had not encountered any Diesels that had something like the Ball Pin in the Prechambers. I finally got to see a Prechamber when I helped one of the Members pull his from a scrap Cylinder Head. What I decided is that the Prechamber is made with the little holes because the designers wanted to control and direct the combustion where they wanted it to go. Also during compression squeezing the Air through those little holes must create some serious turbulence/velocity; and even more so at higher speeds. My comment concerning the Piston weight has more to do with the weight difference of the Pistons at higher speeds due to inertia. My thought on the pre-heated Piston Head is that ounce the Engine is up to operating temp the Head of the Piston (and maybe even the Cylinder walls) is much hotter from absorbing the heat from combustion than the Air Compressed by the Piston is. So I do not think the Piston Head is robbing any heat from the Compressed Air.
__________________
84 300D, 82 Volvo 244Gl Diesel |
#140
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going too far with "opening" the PC will reduce the efficiency of the PC in terms of turbulences and "kept pressure in the PC". I was told on the other hand that above 250 hp the PC becomes the bottle neck (C111 engine). Looking at the development of the n/a to the turbo PC it should be increasing the bores and inner volume. The limit of bore diameter of the radial bores is the risk that the end falls off under heat stress. In any case the bore edges should have a funnel like radius. Mainly the axial bore into and out of the PC. "cleaning" the inner walls of the PC is also important in my opinion (very high gas velocities).
Tom |
#141
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What I meant by the "preheating of the piston and head” is that the piston and head are needlessly subjected to higher heat levels, (during non-power generating periods), for a longer period of time, instead of being able to cool with lower temperatures. The power losses are from having to compress the extra air in the cylinder that could not get into the Prechamber.
The Prechamber design was employed by MB for reasons that they had. They work fine in low boost and low fueling quantities. My intention is not to make a Prechamber, rather I want to end up with an external constant volume combustion chamber that is connected to the work cylinder by a tube. Very much like an Air Cell Chamber as apposed to a Pre, or a Swirl Chamber. Some of the reasons I give why the Prechamber was used was to address the poor injection quality, long duration of the delivery at higher delivery quantities, and ignition noise. The small holes of the Prechamber maintain a high pressure inside the Prechamber, (post ignition), after the pressure curve drops, (on the downward slope of the curve), to that equal to the start of injection, (ignition), pressure on the upward slope of the curve. This increased pressure duration is intended to support the continued combustion of remaining fuel after TDC, and help reduce emissions (NOX), reduce smoke, and increase operational speed. IMO, given the above theory of operation, storing pressure in the Prechamber for the purposes of combustion, would only be necessary after the end of delivery accurse to late in the pressure curve, so that not all the fuel can be burnt in a pressure environment, grater than or equal to, the Prachamber pressure at the start of delivery. If all the fuel is burnt by TDC, there is no reason to restrict/maintain pressure in the Prechamber that could be used for work. Should, at full power delivery quantities, the end of delivery accrue at a point where the pressure will drop below start of delivery pressures, before combustion of the all the injected fuel is completed, then, and only then, should the Prechamber be designed to maintain pressure to complete combustion. The Prechamber always will have a grater volume of gasses trying to get out of it than get into it. As such, the restriction point of the holes, (hole size), should be selected to flow freely, just up to the additional volume of gasses generated by the fuel quantity which is delivered at the point where the end of delivery accurse too late for complete combustion with in the useful pressure curve. In my case, I am going to shorten the Pulse Width, (length of time the injection takes place), with Modified 10mm Elements, so that even at increased delivery quantities at full power, delivery can be completed as early as 10 degrees BTDC. Additionally, the increased quantity of fuel delivered, along with increased intake air from higher boost, will result in the pressures during combustion being increased, which will take longer to decay after TDC, allowing additional time with in the useful pressure curve for fuel to burn as completely as possible. This theory, I think, is evident by the reports from Tomnik regarding his 7.5mm M pump elements. He is injecting more fuel than stock, and doing so with no, or no additional smoke as the result of the shorter delivery time, (pulse width). With the delivery duration reduced, the only limiting factors to operational speed is the oxygen content of the air, the quality of the injection (atomization), and the burn rate of the fuel it self. My Chambers will flow over twice what the stock Prechamber will, plus additionally intercooler boost pressure will be raised. For injection quality, I will be using custom modified nozzles, and running a pop pressure in the 200 bar neighborhood to attempt to get the most burnable injection straight out of the nozzle. The burn rate of the fuel is what it is. I see trying to make power with a Prechamber like others see using a stock T3 turbo making 25 pounds of boost on a 300D. It can be done, but at the cost of efficiency. Coments? |
#142
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Well, to be honest I can not follow your explanations in very detail because my English is not this specified.
But I learned that begin of injection has to be more or less stock because it is related to diesel fuel specifications more that to end of injection to avoid unburned fuel. I got this information from a professor for diesel engine development after trying "late BODs" without much success. This made me change my ideas of the theory of larger elements. Even with larger elements the BOD is at 24 deg. This means that (in theory) either the amount of injected fuel burns completely within the same time as the lower quantity of fuel burns, just because it is able to (like giving diesel in large amounts into a flame/fire) or this "more fuel within the same time" does burn longer with the same intensity (like giving wood to a flame/fire). Now the question is how much fuel can we inject within shorter or same time until we get to the point where the "flame/fire" is not strong enough to burn it with higher intensity. Is it the strength of ignition conditions like compression temperature and spray quality of the nozzle or is it the lack of air at some point? Only the spray quality increases with only lager elements. The pressure peak is higher, more fuel within shorter time. This is why I would not raise the pop pressure this high without having an idea of peak pressure in the lines or even having the nozzle as an orifice and the moved fuel can not leave the nozzle within the stroke of the plunger. This would expand the lines and the end of injection gets undefined. On the other hand I made unexpected high power gains with a n/a 617 engine of a friend. Extreme knocking under throttle and power loss under load was the result of too much full load adjustment. After we turned back the screw the car runs like my SD when it was stock. His coupe is a 4-manual with short rear end but the acceleration is impressive. Out of this lack of air is not the limit #1. Interesting to know what quantity the pump is now set to. This is the quantity this engine can handle with 7.5mm elements to perform like this. Now doing the same with your 10mm elements and see how far you can go with full load setting until black smoke starts regarding quantity and performance. For this test only the plunger diameter is counting. If it turns out that there is kind of limit for the plunger diameter (which is directly connected to duration of injection) then your pre chamber mods come into play. Can the "strength of ignition" be increased with your pre chambers? Can then more fuel be ignited to burn more intensively? These are my thoughts on larger element theory for the future. Up to now I am happy with the performance gains the Floyd elements bring... Tom |
#143
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Lets see what modified prechambers do at dyno.
http://jeemu.kuvat.fi/kuvat/Hammer/Moottori%20OM605ST/stock%20vs%20modified.JPG/full Bigger injection pump elements, more power at same quantity off fuel. spray time is faster and that has big difference at power.
__________________
E21 550hp diesel http://jeemu.kuvat.fi/kuvat/BMW+E21+%28diesel%29/ w202 m104 1000hp with BIG turbo project |
#144
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Compression temperatures relate to the combustible conditions at BOD. The oxygen content plays a huge part in the sustainment of combustion, as does the pressure curve because as the pressure goes up quickly, so does the environment temperature. That helps convert fuel into a burnable condition. Quote:
I am going to open up the nozzle diameter by about 25%, ( I have not done the actual calculations yet to settle on a specific size yet). My concern about using stock nozzles and pop pressures is that because of the faster pressure rise and the increased quantity of fuel that needs to flow in a shorter period of time, that a pressure/volume surge will cause the pintle to be throne from its seat, raising higher, and as a result a denser fuel stream will be created. The denser fuel will take time to evaporate/atomize before it can ignite and that is why the nailing accurse. My thinking is that with a larger nozzle area, a larger quantity of fuel can pass with the same amount of pintle lift. Because of this, when the pintle does lift, the line pressure will drop fast and have to rise again to pass more fuel, (this would happen very fast, injector chatter). I am thinking that the higher pop pressure setting will have two effects. First the frequency of the pintle chatter should be faster, and the pintle should not raise up as far, and second, the average gap that the pintle and nozzle create will be tighter so the higher pressure fuel will create a very fine fuel fog as apposed to a spray. This may be achievable at lower pop pressures, but I am looking a some of the newer common rail systems and they have crazy high pressures. Also the delivery valves should help stabilize the line pressures. They may need to be looked at. Quote:
My chambers will allow more air to be compressed inside prior to BOD. This will raise the pressure and temperature at BOD compared to the pressure and temperatures of a stock prechamber at BOD. Is that what you were asking? |
#145
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I have run enlarged holes on my 300DT, (sold it with them in it actually). I did not touch the IP as I was looking to identify any differences in engine operation. I was surprised at the torque increase. Given how much you are pushing your 605, I expect to see at least 15% to 20% HP/Torque increase across the board, with a shift in the torque curve. You may have to play with the IP timing to find the sweet spot. I am very interest to see how your car reacts to just the enlargement of the holes. Oh yes, is that a thermal coating on the OUT SIDE of the Prechamber? If so I would be afraid that the coating will reduce the heat transfer from the burn tube to the head, (prechamber cooling), and raise the prechamber body temperature to a point where it becomes week. I am going to coat the inside of mine. Just a thought. Keep up the good work!!! |
#146
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Hello. Those not have coatings.
__________________
E21 550hp diesel http://jeemu.kuvat.fi/kuvat/BMW+E21+%28diesel%29/ w202 m104 1000hp with BIG turbo project |
#147
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Is the pressure inside the PC the same as in the cylinder before BOD? In theory increasing the inner volume of the PC will decrease the compression pressure (and the pressure in the PC) and lowers the environmental conditions for ignition rather than getting more. What is your theory behind increasing the inner volume of the PC? I have the same feeling but don't know why. There is more air to be compressed but to a lower pressure so the heat will not raise. I understand that increasing the bores will help to "fill" the PC and also to exit the energy at and after BOD. But my basic question is if the PC acts like a pressure reservoir with a delay in filling and (needed) delay in spraying out the flame to create a smooth and lasting pressure curve in the cylinder. Increasing the bores, mainly the axial one decreases the swirl energy in the PC, in theory. But it seems not to be the case. Tom |
#148
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The stock Prechambers do not flow enough to allow the pressure in the prechamber to come close to matching the cylinder. Quote:
However it might work out that if I can get more air into the chamber before BOD, the additional air and the increased chamber volume may result in the same compression pressures as the stock prechambers that do not allow as much air in by BOD. Quote:
It is my current thinking that the "(needed) delay in spraying out the flame to create a smooth and lasting pressure curve in the cylinder", is required, because with the stock 5.5mm elements, the EOD is so late at higher delivery quantities, that the cylinder pressure drops below the BOD pressure, before the all fuel can be burnt. With 7.5mm and 10mm elements, the injection duration, even at high quantities, will be so short that the EOD could happen as much as 10 degrees before TDC. Because of the earlier EOD, the post EOD cylinder pressures, grater than or equal to the pressure at the BOD, will exist naturally, and will not need to be sustained by a restrictive prechamber. I have seen a couple of studies on swirl chambers and prechambers that say that the size of the restricting holes need to be calibrated to full power delivery quantities at the desired operating speed. I am thinking that as long as we can end the delivery of fuel early enough, that it will burn in a higher chamber/cylinder pressure without the need for "excessive" restriction. In the end, it may proven that some restriction be required. In that event, the restricting only needs to take place at the point where the quantity of delivered fuel can not be burnt before the pressure drops to low. Restricting, (maintaining), the pressure in the chamber prior to that point, is a waste of energy that could be used for work. As for the swril qualtiy, the ball shaft diverts the air flowing out of the burn tube. With an increased volume of air flowing through the same size burn tube the volicity should be higher. The higher volicity air should create a better swril. The small holes are just about 90 dagrees to the burn tube, resulting in individual high volicity currents directed into the side of the larger volume tube. This creates lots of turbulance in the tube at the bottom of the tube, but because the tube is a lorger volume the volicity of the individual currents dies off quickly like a fast moving streem that dumps out into a lake. Additionally, all that high velocity turbulence at the bottom of the tube could have a flow restricting effect during compression filling, as the individual high velocity flows are deflected in all directions when they collide with the tube walls and them selves. To utilize the velocity of the flows, they would each need to be directed smoothly toward the ball shaft which would create a directed swirl. |
#149
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Would angling the holes in the pre-chamber create a swirl of air entering and gasses exiting and have any advantage?
__________________
Gone to the dark side - Jeff |
#150
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__________________
1982 300SD 180K, rebuilt engine 1973 450SLC Megasquirt 1990 Volvo 780 - 273k 1993 Volvo 240 Wagon - Scrap yard slumber http://www.fuelly.com/sig-us/44619.png |
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