I get that injector temperature cannot exceed the rated temp of the return lines, however, what if the fuel were the same temp as the compressed gasses? this would cause more immediate vaporization and combustion, necessitating timing changes. and not only improving performance, but fuel economy and emmissions, as well. This idea stems from the fact that before the diesel can vaporize well, it hits a wall of hot air and needs to "equalize" in temperature/energy before optimum vaporization occurs. This may be a pipe dream however, as if the fuel becomes too hot, then it will hit a much cooler intake charge and re-condense causing a loss in said performance/economy etc. I am wondering simply from an enthusiasts perspective. The heat shouldn't damage anything, as the injectors are mechanical and nothing there to really melt. what temp is the compressed air when injection occurs anyway??? what temp is the fuel usually?

 

I would think that if the fuel were at that temp already it would become a gas and no longer be able to open the injectors,it would simply compress and never enter the chamber.

 

well, here is where it gets interesting, there should be no air in the lines anyway "although we know that isn't entirely true" see air dog fuel preporator. without air the fuel cannot vaporize ex water in a sealed vessel with no air present will boil at a different temperature, same with diesel. in fact, it will create more pressure, sooner, necessitating the need to retard the timing, as the breaking pressure of the injector is reached, and when it collides with the now semi-same temperature air it will mix more thoroughly and combust better, since energy and time do not have to be wasted mixing them and heating the fuel, this occurs much more quickly, and has less waste heat as the heat that would normally be introduced to the fuel in the cyl/prechamber is introduced sooner the heat is still being used to mix the fuel, but just at a different time. well..... that is the way I'm looking at it.

 

Why are you speaking about boiling in a vacuum and pressure in the injectors in the same breath?
Pressure increases the boiling point of liquids?

Kind of counters my earlier statement,but back to your original idea,the point at which you heat the fuel has to be established.

If the fuel were heated pre-IP,it would boil off before it ever got compressed,if it were heated post IP it would change the timing because of pressure increases due to the expanding medium-also compression creates heat-any idea what the fuel temp already is just prior to an injector popping?

 

Also remember that diesel will expand when heated so in theory you would be injecting less but this may be offset from the other fact that it also thins out when hotter so this will allow for more fuel to be injected. No idea on how this would change the spray patern and atomization of the fuel.

I have heard that too hot of fuel will lower mpgs, and there has to be some reason the duramax has a fuel cooler.

 

Ok, seems like I need some amplifying information here. fuel starts in the tank, is lets say, same temp as outside, so.... 60F; you are right, as the fuels temperature increases it expands, and thins out. it hits the IP at ideally the same temperature, remember that if the viscosity is high AKA: temp is low then more pressure is applied "I use pressure here, because the fluid doesn't compress much" after it leaves the pump, it is much warmer, due to pressure and friction. Let's say it picked up 20 or so F, making it 80F. From there it travels through the lines radiating "or absorbing, depending on engine temperatures etc." heat generally reaching the injectors at at about the same temperature. Now, due mostly to heat soak, from infrared energy released from compression/decompression of gasses just underneath, the injectors are quite warm, even after just a couple of cycles. the release of fuel is a cooling process, like sweating on a hot day. the fuel then has the long "in terms of hundredths of seconds" process of absorbing the infrared energy to break down, into an atomized form "ideal would be vapor", and mixing, and re-combining, chemically with the now very excited intake air. Any fuel left over after this process is returned from the return lines coming from the injectors to the tank, or back into the IP feed line. the idea, is to try to use the otherwise wasted heat "an internal combustion engine is an air and heat pump" to heat the fuel to at or near the temperature of the compressed air, to 1: lower the amount of fuel necessary to complete the power stroke, 2:lower emissions, by utilizing more of the available fuel, as it will vaporize, mix, and recombine more easily "due to it's relative temperature", and with more time to do so. 3: lower emissions, by making combustion more complete, and less waste fuel "soot, NOX, ETC." to give an example, sugar "a solid" doesn't mix well with water at room temperature, however, if we add some infrared energy, AKA heat, this is much easier, and takes far less time to do. In a similar fashion, we are introducing a fluid into a gas, and attempting to force them into mixing like water and sugar at room temp, we already produce heat "infrared energy" so we just use that to make it easier to mix and recombine. follow me now.
SUMMARY:
we need to start with cool fuel, to maximize the pressure of the IP and the lubrication factor, o prevent wear and tear on the pump "possibly shielding the pump from heat?"
heat the fuel post pump, pre injection, to increase the pressure in the line, since the pump will act as a one-way valve it cannot go back the way it came, but timing will have to be adjusted due to the increase in pressure due to heat "via a heat switch?" probably easier on a ds4 pump, but not impossible on a mech pump. and the amount of fuel will also have to be adjusted when the temp increases the engine will need less fuel to do the same amount of work, otherwise you will end up with inconsistent EGT's and black smoke.
finally a way to regulate the temperature of the fuel, first by preventing the fuel from getting hotter that the intake charge, and second by cooling any leftover fuel so it cannot effect the fuel coming into the IP and undermine the overall desired effect.

I have thought of a way to do this, it sounds complicated, but I assure you, most propane injection systems today are more complex then this.
yes, this will make more power, yes this will lower emissions, yes this will increase fuel economy. I am not sure of the effect on longevity, but knocking will be down, due to a more smooth combustion, so I assume the violence on the bearings will prove better longevity, but I have yet to build or test this.

---AutoMerged DoublePost---

that is due to the fact that now, the fuel is hotter than the air, and this is dually bad because the fuel is hot pre injection pump, lowering the amount of fuel that gets to the injectors, it isn't vaporizing because it has to equalize with the temp of the compressed gasses before it can ignite properly, this takes time, which is why it loses power, and the pump has to work twice as hard to get the pressure up to get enough fuel packed into the injector for an injection event. so it naturally dumps more fuel, this is hard on the pump as well, the lubricity of the fuel is super low at this point which causes more wear, due to the higher temp fuel being thinner introduced to the pump. The key is higher temp fuel, but at the right time. timing is key here, cool fuel to the pump, the colder the better, hot fuel just before injection, but it has to be right at or just below compressed intake temps, to have the best effect, how much you ask? well, if I knew that I wouldn't have started this thread.

 

I am not so sure about this smoother combustion less knock theory. If the fuel is hotter when it is injected it will all burn up more rapidly causing a higher pressure spike and the common diesel noise will be more pronounced. The common rail engines are quieter due to the pilot injection but turn it off and it rattles bad. Turning up the heat will make the fuel burn faster not slower. If it burns up too quickly then it won't have time to work on the piston as long as cooler fuel does. This could work against the efficincies of the engine. You want this pressure spike to be where it will apply the most energy to the rotation of the crank and not into the rods and bearings. Quick short pressure spikes are good at building rpms but long pressure spikes are better at making torque. I believe that some gain can be made with fuel temps but I don't think you need to make it as hot as I think you are saying and the gains are not likely to be enough to be worth it. I think you are better off playing with fuel pressure and timing.

 

I "think" this is commonly misunderstood with diesel engines. Burning faster or slower won't matter, the reason being as long as it burns. you do not want it to burn long, because that will give too much time for the pistons, cyl. walls, and valves to absorb energy, the less waste produced, because of the use of overall said energy the more "energy" efficient the engine becomes. The other reason is because you are heating air, and making it move, hence my previous statement "ICE is an air and heat pump" the force of heat and expansion from combustion will drive the power stroke. Besides, it will still burn "somewhat" slowly, Ideally you want a vapor. Diesel process, in particular the IDI process, for more reasons than just pilot injection, is unique. think of the prechamber as a pulsejet, fuel is injectedand the majority of the volume of air is located here, and begins to burn/recombine, chemically with the available fuel, as it burns, it attempts to expand, forcing it's way out of the nozzle in the prechamber, by doing this it forces the air remaining, not in the prechamber to cycle int other prechamber to recombine/burn with any remaining fuel, we say that this happens slowly, but that is comparatively slowly to gas engines, and this is only because of the volatility of the fuel involved. to compare, gas engines have slow"er" moving intake gasses, and fast"er" moving exhaust, which is why EGT's don't matter, and oil coating the cyl walls is far less important than in a diesel. with diesels, the inverse is true, slow"er" moving exhaust gasses will cause your head to ...... well, create a small foundry under your hood, if left unchecked. the reason direct injection works better is higher injection pressures and more even distribution of fuel throughout the gas. IDI is superior based on point of principle, which would you think produces more power, a burn barrel that you toss gasoline into periodically, or a jet that burns violently and quickly??? "pulsejet" I agree, the idea of using fuel temperature as an advantage is because I want "higher" pressure, and better "timing" changing the fuels temp is effectively doing both, and I guess we won't know until we try as far as I know, no one has explored this aspect. How much torque/HP would it take to convince you? 1, 10, 50? there are people who spend thousands to get just a couple thenths of a second off of their 1/4 mile time and you say it isn't worth it? like I said, yet to be seen. This is not a pipe dream, I was hoping to get more input here, basically to quell my curiosity, but also to quench my own disbelief that this will work. I still don't know if it will. The diesel rattle is because of the violent slow reaction that occurs over and over due to the constant burn, you think is beneficial. I am not so sure it is. we could both be right, I hope I'm wrong, I am not blasting anyone here, but some one chime in with some engineering and make me pee myself please I have no degree, and can only stand on what I can extrapolate from what I know, and have read. This probably reads like I'm trying to prove something, well, I don't have a chip on my shoulder, but I am curious and want to prove if this works or not. what effect it will have, will it be worth it? I still have my doubts. Thanks for all of the input so far. please correct me here if I'm wrong on something.

---AutoMerged DoublePost---

Diesel engine compression temperature - TDIClub Forums

 

if the burn occurs too quickly then most of the energy will be spent on pushing the crank out the bottom of the engine and the heads off of the top of the engine. You need the burn to happen when the crank angle is going to put as much energy as possible into turning the crank. You might be able to compensate for this by adjusting the timing but you might loose some of that energy out the exhaust. Somewhere between will be that happy medium where the most amount of energy is used on the rotation and least out the exhaust. If heating the fuel will do this then that's great. The point I was trying to make on "not worth it" was more along the lines of too good to be true, if it made measurable gains then I think the auto manufactures would be doing it. Right now they are using higher pressure to better vaporize the fuel. Then to keep it from burning up so quickly they added pilot pulses. The engine actually get better mpgs with the pilot pulse and a slower burn. I am all for thinking outside the box and doing things that others have not ventured into much. I feel that's where most of the good breakthroughs come from. I don't want to discourage you, I just wanted to add my information.

by the way, I was playing around with some of the LB7 injectors a while back. I plumbed one into a 2nd CP3 pump and was pumping about 4,000 psi into it. The return fuel coming out was hot enough to burn and it melted the plastic line I connected to the return side. This was with the injector out side the engines heat. Now with the injectors installed in the engine I imagine that the fuel will be injected at a few hundred degrees or more.

 

I understand, I think it seems here I am getting defensive, it can be difficult to convey your feelings effectively here in text format. I totally understand where you are coming from and I agree, in fact, I think we are mostly on the same page.I am not familliar with LB7 injectors, is that a common rail setup you are talking about? This will only work, with IDI as far as I can think, I don't think it would be feasible with other diesel types, or perhaps there is a way, but without giving away my methods, "possibly patentable" I am not too sure. I think that timing is key, one good solid push downward at the right time, would burn long enough to re-excite the gasses long enough to make it all of the way down the power stroke"remember we are heating gasses here, the hot gasses do all of the work" the decompressing gasses are attempting to leave through the path of least resistance, AKA exhaust they also pull the piston up, just as well as push it down.