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Basic 'how does it work' car question.


Robson
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Hi,

I understand cars to a fairly low level, so I maybe desire a simple explanation of the following,: I understand the fact that a car will require more energy during the time that it starts up, compared to when it's already running. But could anyone explain the more subtle difference between energy use when (a) the car is being started from cold, compared to  (b) the car is being re-started having recently beforehand been running. ?

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Oil, fuel and starter motor.

Oil in cold conditions/climate can be like pancake syrup from a fridge, which makes it more difficult for the engine to spin.

Fuel is less able to evaporate in cold conditions/climate, making it more difficult to burn.

Starter motor has less energy to turn because the battery is producing fewer electrons in cold conditions/climate.

At the moment it is -27°C in Fairbanks Alaska and +24°C in Miami Beach. I'd rather be attempting to start a car in Miami.😉

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Made slightly more complicated if the car is diesel rather than petrol.  Petrol has a spark to ignite the explosion to start the engine.  Diesel, on the other hand, has just the compressive effect of the piston rising up the cylinder with enough force (driven by the electric starter motor) to compress the air and fuel mixture so that it heats up enough to explode.  When the engine and air is cold there is more friction in the moving parts and more energy needed to heat up the air/fuel mixture. (In older diesel engines there was a glow plug to heat up the top of the cylinder to help start the car with pre warmed air).  Once the car is warmer, its easier to restart as there is less friction and the engine block is already warm so the air/fuel mixture explodes easier requiring less energy from the starter.

In the Alaska case by cajal, ordinary diesel fuel becomes gel like after a time at -10°C, so you would not be able to start the engine at all if your car is outside with untreated fuel!!

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3 hours ago, Lehaut said:

Made slightly more complicated if the car is diesel rather than petrol.  Petrol has a spark to ignite the explosion to start the engine.  Diesel, on the other hand, has just the compressive effect of the piston rising up the cylinder with enough force (driven by the electric starter motor) to compress the air and fuel mixture so that it heats up enough to explode.  When the engine and air is cold there is more friction in the moving parts and more energy needed to heat up the air/fuel mixture. (In older diesel engines there was a glow plug to heat up the top of the cylinder to help start the car with pre warmed air).  Once the car is warmer, its easier to restart as there is less friction and the engine block is already warm so the air/fuel mixture explodes easier requiring less energy from the starter.

In the Alaska case by cajal, ordinary diesel fuel becomes gel like after a time at -10°C, so you would not be able to start the engine at all if your car is outside with untreated fuel!!

All modern car/small vehicle diesel engines have glow plugs, one per cylinder, they have two functions, to aid starting in cold conditions, and to reduce exhaust emissions after a cold start in cold conditions when the engine computer works out how long to keep them glowing according to how cold it is.

Bigger diesels in trucks can use inlet manifold air preheaters, a bit like an electric fire element in the inlet manifold to feed hot air to the cylinders as a cold start aid and reduce cold exhaust smoke after the start.

The older Perkins type where a glow plug ignited fuel sprayed onto the glow plug in the inlet manifold isn't used any more - too much smoke etc.

Diesel fuel comes in different grades - winter and summer diesel  For example - the UK changes to winter diesel in November and goes back to summer diesel in March. Winter diesel either has more kerosene in it or has an anti-freezing additive in it to stop the filter blocking with the wax flakes when its cold in the diesel.

Some vehicles have an electrical heater controlled by a thermostat in the fuel filter to stop the filter plugging with the wax flakes.

https://en.wikipedia.org/wiki/Winter_diesel_fuel

https://en.wikipedia.org/wiki/Cold_filter_plugging_point

 

 

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8 hours ago, Lehaut said:

In the Alaska case by cajal, ordinary diesel fuel becomes gel like after a time at -10°C, so you would not be able to start the engine at all if your car is outside with untreated fuel!!

Way back in the day (60's), I recollect seeing a guy with a Kenworth semi in a rest area with a small fire burning away under his fuel tank. Yes - it was a freezing day.

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End of January this year we spent a week in the Les Deux Alpes, drove there in our petrol car.  It stood outside for a week covered in snow (local transport and ski lifts were plentiful).  The night temperature fell to -19°C.  The battery is a stop start one and is 5 years old.  I took jump leads and a starter pack,  just in case.  I have no experience of operating a car at these low temperatures.  Heart in mouth on the day of our departure I went out to start the engine,  wondering (too late) if the engine block plugs were under the car!!.  One push of the button, turned over and started as it does in normal here at Nantes temperatures.  Gone are the days when my uncle keep a lit paraffin heater under his "sit up and beg" Ford Popular to make sure it would start in the morning (the garage burn down one winter).

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