Robot skrev:
it was already posted here before.
Sorry I missed that, but it could benefit of a separate thread than.
Did you see/read the tech paper as well? It has most useful information,
http://delphi.com/pdf/techpapers/2009-01-0615.pdf just like the Bosch flex start-study
Obormot skrev:
those injectors will be aviable in 2010-2011. maybe.
Yes a pity we need to wait, and they will probably not suitable for retrofitting in all cars, but the concept has some advantages compared to heating the fuel rail (like the Bosch flex start):
Citat:
• Significant electrical energy is required to heat
the entire quantity of fuel in a short amount of
time
• Pre-crank warm-up times are approximately 60
seconds at -5°C
• Large radiant heat loss area
• Heated fuel rises to the top of the rail
• First injections consist of ambient temperature
fuel
• Requires pre-crank PCM turn-on strategy and
starter control
Robot skrev:
i just thinking...
1. there is no big difference, what to heat: fuel or air
I think that there are differences.
When the fuel is heated you will get fuel vapor much quicker as when the air needs to heat the fuel first even if the amount of energy is equal.
If it the spray hits a cold engine part it will get much harder for the air to make it evaporate (like heating water with a föhn).
Warming the air has the advantage that you can heat it as much as you like, the fuel can only be heated to just under its boiling point under pressure in the fuel-rail.
Robot skrev:
2. pins on heated injector are tiny - power of heater element is not very big
Yes I noted that to, however we do not know if they are operating at 12V or at a higher voltage.
Anyway according to the tech paper the power is enough to do this:
Citat:
Figure 10 shows the resultant increases in the injector’s outlet stream temperatures (measured with thermos couple located in the fuel stream) above ambient (20°C for the following graphs) with static
ethanol flow (3.4g/s) and 100% heater power.
To heat 3,4g/s of ethanol which has a specific heat of 2.44 J/gK with 20° you would need 3,4g/s * 20K * 2,44 J/gK = 165,92 J/S so they are at least using 166 watt each x 4 = 664 watt, which is not that little, especially if you realize that this is measured in the fuel steam so heat losses from the injector to the surrounding parts, air etc is not included.
At -5°C and with 94% ethanol and 6% water the engine starts after 2,9s cranking without preheating, with 6s preheating it even starts after 1,8s cranking. Also consumption and emissions after the cold start are shown to be much lower according to the paper. I think that is quite convincing that the system works quite good.
It would be interesting to know at how much lower temperatures the system would be able to start a care on pure ethanol. For E85 I think this should be enough already for almost any cold-start.
/Aryan
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