Compression Ignition Engines

While electric cars are starting to gain a following, the vast majority of the cars on the road today are still powered by internal combustion engines.  The two main types of engines used for automobiles are gasoline engines (spark ignition) and diesel engines (compression ignition).  One of the main differences is that in a spark ignition engine a mixture of air and gasoline fumes is compressed, and lit off by a spark at the appropriate time.  In a compression ignition engine, on the other hand, only air is compressed and a fine mist of diesel fuel is injected into the hot air at the appropriate time.

Refrigerators and Cryotherapy

What does a common household refrigerator have in common with a home medical treatment? One answer might be that you get ice cubes out of your freezer to put on your black eye or sprained ankle. There might be other answers surrounding your treatment when the refrigerator tips over on top of you, but in this post we are going to talk about refrigerator operation and cryotherapy.

Duhamel's Theorem, part 2

As an additional example of Duhamel’s theorem that we talked about in the last post, we’ll use the solution to a sudden change in temperature at the surface of a semi-infinite solid to examine the temperature in a thin layer in the wall of the cylinder of an internal combustion engine.

Leveraging Solutions with Duhamel's Theorem

There are many transient heat transfer problems that can be solved analytically for a simple boundary condition, but would be difficult or impossible to solve with a more complicated, time-dependent boundary condition. In many cases, if the original solution can be formulated, possibly through parameterization, as the response to a unit step change on the boundary, Duhamel’s theorem can be used to extend the simple solution to a more complex case.

The Standard Atmosphere

Most people don’t need to worry too much about the temperature and pressure of the atmosphere, as long as there is some of it there to breathe.  However, pilots, airplane designers, meteorologists, and many other people need to know how the temperature and pressure typically change with altitude.  Of course, on any given day at a particular location, conditions might be different than the “typical” condition.  Still, the typical conditions are useful enough that there are several definitions of the Standard Atmosphere describing conditions clear out into what is usually considered outer space.

Fortuitous Properties of Cold Water

As cold water starts to get close to the freezing point, it behaves differently than most other substances in that it stops getting denser and actually gets less dense as it gets colder.  In this post, we’ll look at the variation of density with temperature, and talk about why it is lucky for all life on earth that it behaves this way.

Specific Heat Ratio

The specific heat ratio, k, is defined as the ratio of the constant pressure specific heat to the constant volume specific heat.  It depends weakly (over small temperature ranges) on temperature.  In this post, we’ll look at the effect of that temperature dependence.  This figure shows the value of the specific heat ratio of air as a function of temperature.