In the Otto cycle, the fuel/air mixture is...

🔍 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

In the Otto cycle, the fuel/air mixture is ignited at what point and by what means?

At TDC by heat generated by compression.

Just before TDC by heat generated by compression.

Just before TDC by spark ignition.

At TDC by spark ignition.

🔍 Key Concepts

💭 Think About

✅ Before You Answer