Team-BHP - Common Rail : Why is cold start tougher at higher altitudes

Quote:

Originally Posted by tsk1979 (Post 2896100)

I was at a higher altitude, with lower night temperature. (4400+), I guess at that altitude, even slight increases in altitude can have an effect

I'm talking about Korzok, Tso Moriri, at ~4550m. (15,000'). Lowest night temp. (-)2*C, ambient at engine start was +1.5*C.

Quote:

Originally Posted by SS-Traveller (Post 2411172)

Highest altitude where the Scorpio mHawk engine was started by me, was at Korzok (Tso Moriri) on 15 June 2011 - altitude close to 15,000 feet. Engine started at 6 AM after overnight parking in open (no precautions or blankets etc.). The minimum temperature readout on the thermometer inside the car showed (+)1.5*C. No diesel gelling had occurred - stored cans of diesel in the back of the car were quite fluid. Diesel in the tank was treated with BG247 additive @1ml/litre approximately.

Attachment 569377

Starting results: Engine fired with one long 5-to-7-second crank, emitted one puff of light smoke, and settled into normal idling.

Edit: Sheesh... this is sounding like a mine's bigger than yours argument... :p

Quote:

Originally Posted by SS-Traveller (Post 2896141)

I'm talking about Korzok, Tso Moriri, at ~4550m. (15,000'). Lowest night temp. (-)2*C, ambient at engine start was +1.5*C.

Edit: Sheesh... this is sounding like a mine's bigger than yours argument... :p

I was just guessing.
So maybe its not the engine block issue. Maybe something to do with filters. For example, if ice crystals for in sedimenter, fuel delivery will be blocked. I had to manual prime the hand pump to get fuel, and then start.

Does formation of ice crystals depend upon altitude?
Or is it that fuel at leh has higher water content which can lead to more water in sedimenter?

Quote:

Originally Posted by tsk1979 (Post 2896174)

Or may be it is "BG247 additive @1ml/litre approximately" which prevented gelling and crystals in case of SS_traveller just a wild guess.

Quote:

Originally Posted by vibbs (Post 2895348)

Pardon me for butting in, but are we seeing a loss in compression here? Its just that the final pressure is less owing to less initial pressure, doesn't the ratio remain the same? So IMO there is no loss of compression or CR. Or am I missing something here?

That comment was with respect to

Quote:

Originally Posted by Off Roadie (Post 2894242)

Just adding a link to a PDF file that supports the point that loss of compression results in starting issues.

Quote:

Originally Posted by vibbs (Post 2894541)

Loss of compression in typical sense affects combustion because it fails to raise the temperature beyond the self ignition temperature of fuel.

CR (and expansion ratio) is a hugely important parameter, and a lot of equations are recast in terms of it. These equations all assume that there is no leakage. The amount (mole) of gas you start of with is what you end up with. When this assumption is no longer true, the equations have to be modified. One of the changes is a new 'effective CR' value.
The actual CR, as defined by initial volume/ final volume is mechanically set, and ofcourse remains unchanged.

Regards
Sutripta

BTW, you might want to revisit the stoichiometric part. Just a thought.

Quote:

Originally Posted by vina (Post 2895852)

Dada, what derivation do you want,

I was thinking of a textbook style explanation, starting almost from the beginning. You are right, actually not necessary. If we use the Wiki article as a base, hardly anything needs to be explained.

Practical engines are way different from our idealized, simplified models. Yet an understanding of that is an essential foundation.

Regards
Sutripta

Quote:

Originally Posted by Sutripta (Post 2896352)

That comment was with respect to

CR (and expansion ratio) is a hugely important parameter, and a lot of equations are recast in terms of it. These equations all assume that there is no leakage. The amount (mole) of gas you start of with is what you end up with. When this assumption is no longer true, the equations have to be modified. One of the changes is a new 'effective CR' value.
The actual CR, as defined by initial volume/ final volume is mechanically set, and ofcourse remains unchanged.

Regards
Sutripta

BTW, you might want to revisit the stoichiometric part. Just a thought.

Was expecting you to point that out sooner =)
Promise you will give you a proper text book reply once I am on land.

Since I am really not aware about the ECU and all its parameters, maps (tables), I am staying out of it. If a Tata or Mahindra tech tell me/us that the ECU checks xxxxx I will take their word otherwise we are just guestimating.

I think there is a lot of combination of factors at work here. The surface friction between the injected, high velocity fuel particles and compressed gas may also play a part here.

So will do it with a cool head on land. Doing it all, over a cellphone is really challenging.

Quote:

Originally Posted by Off Roadie (Post 2896551)

Was expecting you to point that out sooner =)

Normally don't react to opinions. ('Facts' is another matter!)

Quote:

Promise you will give you a proper text book reply once I am on land.

Sorry. Beyond my level of competence, and too lazy.

What happened to your own textbooks?

BTW, DMET?

Regards
Sutripta

Quote:

Originally Posted by PGA (Post 2895185)

Your concept is absolutely in order. However converting it to practicality for ordinary vehicles may not be a great idea as benefits may not offset the penalty imposed by additional mechanical complications.
Anyway the problem is not of starting at all but only that off delayed lightup.

Infact, as brought out in the earlier posts by Offroadie, similar concepts are used to start bigger engines like the ones fitted on the ships and also those fitted on heavy earth moving machinery and aeroplanes. These are called turbostarters.
Cheers

@ PGA, Excellent Posts. I think the Ones used in Earth bound machinery are called Super Chargers and use an engine operated piston compressor to store air in a seperate cylinder which is useful in starting as well as providing optimum intake pressure regardless of engine RPM. Piston powered aircraft also had super chargers but to save on cylinder weights they used explosive caps attached to intakes for starting on ground. Modern piston aircraft have starter motors and fire up only one cylinder, which then fires up rest of the engine.

Regards

Quote:

Originally Posted by SR71A

Thanks for the appreciation SR71A.

You are quite right about percussion caps firing to ignite the aviation engines of yore.

Superchargers are akin to turbochargers for the purpose they are meant for but mode of operation varies. Superchargers have almost given way to turbochargers nowadays.

Aviation technology of 70 and 80s has come into cars in last decade or so. Driven by severe emission norms of various goverments, engines have to be run more and more efficiently. Thus comes a need to govern them more efficiently which is beyond the capacity of open loop mechanical systems. Therefore you have microprocessor based ECUs. They are not full authority as yet but to meet the norms of near future they would need to evolve very fast to available technological standards. Even today you have ECUs fitted on Indian cars which can dynamically control valve timings, ignition timing, mass flow rates and some more engine governing inputs.
Cheers

BTW your handle reminds me of one of my favourite machines, the Lockheed Blackbird. One of the greatest machines ever built.

Quote:

Originally Posted by PGA (Post 2898977)

Thanks for the appreciation SR71A.

BTW your handle reminds me of one of my favourite machines, the Lockheed Blackbird. One of the greatest machines ever built.

@ PGA ; Though Off Topic, SR71A is indeed the nomenclature used by Lockheed Aircraft for the legendary Blackbird. One of my favourite aircrafts among many

Again on topic. It will be some time before we see FADEC on day to day automobiles. But it will be great if run of the mill ECUs can be programmed to take care of weather extremities.

Again after going through the thread it is apparent that the problem is experienced by only a few types of vehicles and that too not by all the users under similar conditions.

I have been informed that sometimes ECU software will get "stuck" on an erroneous map due to some software error. (These programs are not more advanced than MS Windows!). I have tried to get over the problem by insisting on a reset of ECU to factory settings on all my service visits for my swift DDis. I dont know whether it is advisable for all, but that is one thing that can be tried.

Happy MOtoring.

Quote:

Originally Posted by SS-Traveller (Post 2893226)

I have personally not faced any cold start issues, but I do use a diesel antigel product in high-altitude low-temp regions. Hate working too hard to start an engine, if preemptive measures can be taken to ease such efforts.

Here is my take.

At higher altitude, with lower atmospheric pressure, the waxes in the diesel fuel tend to precipitate in cold weather. So there is less fuel going into the cylinders initially (may be due to congestion in the line/filter), after a few cranks there is sufficient fuel to start the combustion. The fuel line clogging must be miniscule and would get cleared once the line is constantly pumping fuel.

That may be the reason that the antigel ensures an instant start.

As far as Laura starting, they for all you know; have designed the fuel lines/filters for European low temperatures, which can regularly hit -30 degrees in winter, sufficient to play havoc if the wax clogs up narrow passages. Just my guess. Some one who has studied the fuel delivery systems in WV and Indian cars can comment on it with more authority.

Quote:

Originally Posted by Aroy

Here is my take.

As far as Laura starting, they for all you know; have designed the fuel lines/filters for European low temperatures, which can regularly hit -30 degrees in winter, sufficient to play havoc if the wax clogs up narrow passages. Just my guess. Some one who has studied the fuel delivery systems in WV and Indian cars can comment on it with more authority.

Ooty is not really high altitude in terms of location but for what it is worth, my Yeti started first crank the other day after sitting out in the cold all night. It was switched off and outside from 930pm to 9am. The temperature that night was about 7 degrees at its lowest ebb. Anyway it was cold enough to warrant a roaring fire in our room.
I don't think that a car designed for European cold temperatures will have any trouble handling our scenarios here, except maybe in the depths of winter in the Himalayas somewhere.