🔍 Key Concepts

• Otto cycle vs Diesel cycle – which one uses spark plugs and which one relies on heat of compression • Top Dead Center (TDC) – what is happening to the piston, pressure, and temperature near this point • Ignition timing – why ignition might occur slightly before or exactly at TDC in a gasoline engine

💭 Think About

• Ask yourself: in the Otto cycle (gasoline engine), is the fuel/air mixture supposed to ignite because of compression alone or because of an external device? • Consider what engineers try to achieve with ignition timing – should the maximum pressure occur slightly after TDC or exactly at TDC for best efficiency? • Think about which cycle (Otto or Diesel) is associated with ‘compression ignition’ and which with ‘spark ignition’

✅ Before You Answer

• Confirm whether the Otto cycle is defined as a spark-ignition or compression-ignition cycle in your engineering text • Check what point in the piston’s travel typical gasoline engine ignition occurs: slightly before or exactly at TDC • Eliminate any choices that describe the wrong ignition mechanism (heat of compression vs spark plug) for the Otto cycle