Engine Block Heaters and Battery Heaters

Posted by PITHOCRATES - February 19th, 2014

Technology 101

As Matter loses Heat it shrinks from a Gas to a Liquid to a Solid

There is no such thing as cold.  Cold is simply the absence of heat.  Which is a real thing.  Heat.  It’s a form of energy.  Warm things have a lot of energy.  Cold things have less energy.  The Kelvin scale is a measurement of temperature.  Like degrees used when measuring temperature in Celsius or Fahrenheit.  Where 32 degrees Fahrenheit equals 0 degrees Celsius.  And 0 degrees Celsius equals 273.15 kelvin.  Not ‘degrees’ kelvin.  Just kelvin.

When something cools it loses heat energy.  The molecular activity slows down.  Steam has a lot of molecular activity.  At 212 degrees Fahrenheit (100 degrees Celsius or 373.15 kelvin) the molecular activity decreases enough (i.e., loses energy) that steam changes to water.  At 32 degrees Fahrenheit (0 degrees Celsius or 273.15 kelvin) the molecular activity decreases enough (i.e., loses energy) that water turns into ice.

The more heat matter loses the less molecules move around.  At absolute zero (0 kelvin) there is no heat at all.  And no molecular movement.  Making 0 kelvin the ‘coldest’ anything can be.  For 0 kelvin represents the absence of all heat.  As matter loses heat it shrinks.  Gases become liquid.  And liquids becomes solid.  (Water, however, is an exception to that rule.  When water turns into ice it expands.  And cracks our roadways.)  They become less fluid.  Or more viscous.  Cold butter is harder to spread on a roll than warm butter.  Because warm butter has more heat energy than cold butter.  So warm butter is less viscous than cold butter.

Vehicles in Sub-Freezing Temperatures can Start Easily if Equipped with an Engine Block Heater

In a car’s internal combustion engine an air-fuel mixture enters the cylinder.  As the piston comes up it compresses this mixture.  And raises its temperature.  When the piston reaches the top the air-fuel mixture is at its maximum pressure and temperature.  The spark plug then provides an ignition source to cause combustion.  (A diesel engine operates at such a high compression that the temperature rise is so great the air-fuel mixture will combust without an ignition source).  Driving the piston down and creating rotational energy via the crank shaft.

For this to happen a lot of things have to work together.  You need energy to spin the engine before the combustion process.  You need lubrication to allow the engine components to move without causing wear and tear.  And you need the air-fuel mixture to reach a temperature to burn cleanly and to extract as much energy from combustion as possible.  None of which works well in very cold temperatures.

Vehicles operating in sub-freezing temperatures need a little help.  Manufacturers equip many vehicles sold for these regions with engine block heaters.  These are heating elements in the engine core.  You’ll know a vehicle has one when you see an electrical cord coming out of the engine compartment.  When these engines aren’t running they ‘plug in’ to an electrical outlet.  A timer will cycle these heaters on and off.  Keeping the engine block warmer than the subfreezing temperatures.

The Internal Combustion Engine is Ideal for use in Cold Temperatures

At subfreezing temperatures engine oil because more viscous.  And more like tar.  This does not flow well through the engine.  So until it warms up the engine operates basically without any lubrication.  In ‘normal’ temperatures the oil heats up quickly and flows through the engine before there’s any damage.  At subfreezing temperatures oil needs a little help when starting.  So the oil sump is heated.  Like an engine block heater.  So when someone tries to start the engine the oil is more like oil and less like tar.

Of course, for any of this to help start an engine you have to be able to turn the engine over first.  And to do that you need a charged battery.  But even a charged battery needs help in sub-freezing temperatures.  For in these temperatures there is little molecular action in the battery.  And without molecular activity there will be little current available to power the engine’s starter.  So there are heaters for batteries, too.  Electric blankets or pads that sit under or wrap around a battery.  To warm the battery to let the chemicals inside move around more freely.  So they can produce the electric power it needs to turn an engine over on a cold day.

Once an engine block, the engine oil and battery are sufficiently warmed by external electric power the engine can start.  Once it warms up it can operate like it can at less frigid temperatures.  The engine alternator powers the electrical systems on the vehicle.  And recharges the battery.  The engine coolant heats up and provides heat for the passenger compartment.  And defrosts the windows.  Once the engine is warm it can shut down and start again an hour or so later with ease.  Making it ideal for use in cold temperatures.  Unlike an electric car.  For the colder it gets the less energy its batteries will have.  Making it a risky endeavor to drive to the store in the Midwest or the Northeast during a winter such as this.  Something people should think about before buying an all-electric car.



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