gruntguru wrote:I just had another thought. Reducing the pressure in the lines will cause lighter components of the fuel to vaporise if the pressure is reduced below the vapor pressure of that component. This would potentially allow ALL THE FUEL between the flow meter and the pump at the engine to be used for a short term power boost.
gruntguru wrote:If the scam involves reducing pressure to produce a vapor bubble, you restrict the flow through the flow meter to 100 kg/hr eg with a fixed displacement pump or throttling valve immediately after the flow meter. The lift pump at the engine would need to be capable of pulling fuel from the supply line at less than atmospheric pressure. The vapor would need to have a "high point" in the lines to accumulate so the pump does not see vapor at its inlet. The "high point" would be in a hotter section of the fuel lines (a "fuel heater" probably) to ensure vapor bubbles do not form elsewhere in the lines.
Sorry to prick your bubble - but this is all just so wrong!gruntguru wrote:If the scam uses a vapor bubble, it would be acchived by having LOW pressure in the lines (or more likely the fuel heater). For extra power, the fuel pressure is reduced causing a vapor bubble in the fuel heater and allowing the liquid fuel to be drawn out of the heater in addition to the 100 kg/hr coming from the tank.
Firstly - if you "reduce the pressure in the lines" - you simply inject fuel at low pressure (there is no vaporisation here). So for a given number of holes and nozzle diameter at the injector - you simply have a lesser pressure gradient driving the fuel and hence would need to increase your injection duration to even achieve similar power levels (let alone poorer fuel atomisation)
Secondly - the vapour bubbles you talk about - this is cavitation. If you have a 500 bar fuel pump, and fuel moves through the pipes to the injector - the stagnation pressure in the pipes is 500 bar throughout. You do not need to reduce this to cause vapour bubbles (or pump less than atmospheric like you said). Theoretically speaking - even if the fuel is accelerated so much as the fuel pipes twist and bend to the reach the injectors (narrower cross section - mass is conserved, accelerating the fluid. This increases dynamic pressure at the cost of static) you eventually reach a threshold point where the local static pressure goes less than vapour pressure at the bends causing cavitation bubbles (at those local areas of the bend). But static pressure will recover after the bend. By no means will you have a large scale vaporisation of a whole column of fuel in the delivery pipes due to this. And realistically speaking, I'm not even sure how probable it is for cavitation to happen in the bends and twisty section of fuel pipes - as the flow in these pipes are pulsed, according to your cylinder firing. So at some point all of the pressure in the pipe is static and well above vapour pressure. That's why you have a pressure relief valve and a return oversupply loop in the fuel system to go back to the tank. (This opens to discussion if the teams play with the oversupply loop and short circuit it after the FIA approved flow meter location)
Thirdly - cavitation is bad. You do not want cavitation to occur in your fuel system. Yes, it’s unavoidable to some extent inside the injector, and you get some dubious benefits during the primary breakup mechanism, but these bubbles have a habit of imploding upon themselves - sending shock waves through the liquid and severely damaging metal, corroding them. And even if they manage to agglomerate and grow, rather than burst and get through the injector - it causes poor fuel delivery, introduces uncertainties in combustion and potentially unbalanced cylinder pressures in the engine.
The presence of large scale vortices (relative to nozzle diameter) have known to create cavitation in the bulk of the fluid without any geometric means (like bends) but this is erratic and a very poorly understood phenomena, let alone exploit it to gain benefit. And we are still talking about two phase flow here - and not a complete vaporisation of fuel column.
Fourthly - if you "potentially allow ALL THE FUEL between the flow meter and the pump" to evaporate a choice has to be made during hardware selection if one is going to use spray injectors or gas injectors. (Not sure if possible - the injectors have to be FIA approved) The nozzle diameters, injector capacity are different between the two (because energy density for a given injection volume is different between liquid fuel and gaseous fuel - you need to pump more gas to achieve similar power levels as liquid) that you cannot have one doing the job for the other - and a compromise would result in a mediocre combustion system.
