While Minnesota State University, Mankato purchases bulk electricity from a local utility it utilizes diesel generators for certain electrical power needs. Two Katolight diesel generators are installed in the main utility plant for emergency power (shown below). The emergency power is only used for fire alarms, flood lights, and for areas of the school which require constant power during a local power outage. For other power needs, three Caterpillar diesel generators are installed in a separate generator building for stand-by power applications. As mentioned in the Facilities Overview, the University receives reduced electricity rates by allowing curtailment of the campus load. During times when electrical power is in high demand, Minnesota State will go “off” the local electrical grid and create its own electric power via the three stand-by generators (shown above). In exchange for this, Minnesota State is charged a reduced amount for its electric power consumption.

traversing the full cylinder displacement during one half rotation of the crankshaft. The four strokes are intake/induction, compression, power, and exhaust.  However, the diesel engine (shown below) is approximated in most texts by modeling it as a four process cycle. The first process is compression of the cylinder air.  Next is a heat transfer process representing the ignition of the fuel creating heat addition and the power generation (i.e. the air expands). The third process is continued power generation as the air finishes expanding. The last process is a heat transfer to reject waste heat and prepare for the next cycle.  Notice that the thermodynamic approximation ignores the intake and exhaust strokes.

Process Diagram of 4 Stroke Diesel Engine [7]

In contrast to a gasoline engine which uses electrical ignition of the fuel, diesel fuel “self ignites” due to higher pressures and temperatures in the cylinder after the compression process.  It is not uncommon to model these steps as adiabatic and reversible, implying they are isentropic (constant entropy).  In other words, heat transfer out of the cylinder wall is ignored and loss factors such as friction are ignored.  It doesn’t take a “diesel engine brain surgeon” to recognize this is not realistic; however, it does give us a starting point for diesel analysis.