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-   -   Common Rail : Why is cold start tougher at higher altitudes (https://www.team-bhp.com/forum/technical-stuff/85817-common-rail-why-cold-start-tougher-higher-altitudes-4.html)

^^^
Tanveer, what is your observation on the starting characteristics of direct injection, but with jerk pumps, not common rail engines at high altitudes. As used on commercial vehicles.

Regards
Sutripta

Hi Tanveer,

Indeed its the cold diesel in the tank that is to be blamed.

Diesel can get quite thick at -5, almost like thick tomato soup.

You may have noticed truck drivers "heating" the tanks with a small fire underneath. This is the reason for the same.

The rail pressure in the current generation common rails (whats referred to as system pressure) is of the order of 1600 bar (1600 times atmospheric pressure). When a fluid is compressed as much, it naturally gets heated. So its not diesel in the rail.

The CR pump gets the diesel from the feed pump. When enough diesel does not reach the CR pump, and the injector starts injecting fuel when you crank up the engine, the rail pressure falls and the engine does not start.

Cars in cold countries have electric heating arrangement. Parking lots are provided with electric sockets and the car can be plugged in to keep the oil and diesel warm.

We can't draw as much power from our regular batteries, sadly, neither can we risk heating the tank with a fire.

As an experiment, when you go to some cold place next time, you can keep some diesel in a glass jar outside and check how thick it is next morning :)

check out the last product on this page:
http://www.frybrid.com/parts.htm#heat

I think you did not read the thread, or even its title. We are wondering why at -8 vehicle starts without issues even at 2500mts, and at -1 at 4000mts there is trouble starting.
Sure diesel should gel up more at -8 rather than at -1, right?

The hanle observatory has a TCIC Tatamobile, which started without any issues. Moreover, local non common rail taxies(Mahindra DI engine I think) do not have starting trouble in summer season

^^^
Couple of hypothesis, but really need to talk with the development engineers who did the high altitude testing/ validation.

Star_Aqua, where art thou? (Even though the Safari has Delphi systems)

Regards
Sutripta

Did you get some answers.
I guess I need something which will bring down diesel "gel" temp by around 5-6 degree C.
I do not want cetane modification blah blah, just something to enable start at -2/-3 kind of altitude.

Diesel is not the same everywhere. High Altitute / Low Temp diesel has some 'anti-freeze' in it. Also, remember at altitude the compression in a cold engine at starting will be lower in psi terms, reducing the charge temperature even further.

At Gangtri, I had diesel filled from the "plains". So no anti freeze added. Yet, with overnight temp of -8 (it had dipped below zero in the evening,fallen to -8, and risen to -6 at around 8am, I could get a first crank start.

However, in altitudes above 4000m, even with min temp of 2-3 degree C, starting is an effort.

I think It has something to do with compression?

I know this was discussed earlier but is the lack of oxygen (comparatively) at higher altitudes completely ruled out?

Tanveer - from your experiences, has something like this occurred when the temperature outside was... say 15 degrees C. What I mean to ask is, is this problem pertinent only when it is extremely cold (0-10 c) or does this happen in slightly higher temperatures too?

Problem starts happening when the temperature goes down to 5 degree C or below at high altitude.
At low altitude (upto 3000m or below), even -2 to -8 overnight temperatures are not a problem.
Infact I was pleasantly surprised when the safari started at -8 without any fuss!

I have Scorpio 4WD 2.6L DI Turbo.
When I was in Manali in Oct. 2010, snow fall continue from 12 hours and temp -1 in afternoon.
after 24 hours when the car park and car cover with full of snow. start in first self.
when I was in kaza in April 2011. temp was -7 at 6AM. car start in 3 long self.
slightly long as compare to lower altitude.
so i am not facing any major problem in starting in higher altitude.
when i ask a technician in mahindra, He said in crdi technology fuel pipes near crdi unit is very thin compare to Di technology.
So problem in higher altitude is thinner pipes.
May be he is correct.

I think I'll put faith in the Kabsons LPG stove, a kettle of hot water, and a small high amperage battery charger.

My touring in cold places was with a XD3. Notoriously bad starter. But my biggest problem was not in a place which was coldest!

Your question: I think SS located some pour point depressors.

Regards
Sutripta

Atmospheric temperature being the same.

At high altitudes, lower atmospheric temperature -> lower compression pressure -> insufficient heat produced by compression -> inability of diesel to ignite.
Multiple cranks warm the engine up a bit and thus the diesel ignites.
Hope that clarifies things.

Should have added that the place was Haa. Neither the coldest or the highest.

Unable to understand the point you are trying to emphasise.

Regards
Sutripta

Oops thanks for pointing out, completely my bad it should have been as follows.

Atmospheric temperature being the same.

At high altitudes, lower atmospheric pressure -
> lower compression pressure -> insufficient heat produced by compression -> inability of diesel to ignite.
Multiple cranks warm the engine up a bit and thus the diesel ignites. Hope that clarifies things.

Edit:
Can someone report my post above, somehow I do not have that option available on the mobile browser.

Hi,
insufficient heat = lower temp?
Could you give some illustrative values, (and if possible the basic equations) which lead to these results.

Regards
Sutripta