internal combustion engines

internal combustion engines

1. Engine definition: a device which does work, no matter how it is powered

   • modern meaning is a device which operates automatically and continuously to convert some form of energy into mechanical power

2. Typical Engine Process

   • invest work to compress working fluid
     • Inject heat into fluid
       • recover greater amount of work
         • return to initial conditions with removal of heat

3. Engine classification

   • type of ignition
     • Spark ignition: otto cycle si engine remains almost same as 100 yrs ago
       • low cost, high efficientcy, simple/robust, good power/weight ratio
     • Compression ignition
       • air to fuel ratio, high compression ratio, not throttling of intake air, might not have an propagating flame/could have uncontrolled burning
   • Engine cycle
   • basic design
     • si desin simple, robust
   • air intake process
     • CI engines have a wide range of air to fuel ratios
     • throttle: method of controlling how much fuel goes into piston chamber, by obstructing the path of the fluid
   • position, no. of cylinders of reciprocating engines
   • method of fuel input (spark ignition)

4. Engine types

   • 4 stroke SI engine
     • -fuel+air goes in, vol increases
       • as piston reaches almost dead top fuel mix is compressed
         • at ~constant volume fuel is ignited,product gas expands vol increases
           • product gases pushed out of cylinder; volume decreased but pressure relatively similar
   • 4 stroke Combustion engine
     • air intake
       • air compressed, fuel injected just before piston is at dead top
         • fuel ignites and expands doing work
           • combustion products pushed out through the exhaust