🔍 Key Concepts

• Theoretical Otto cycle vs. theoretical Diesel cycle – how combustion is modeled in each • How combustion occurs in constant-volume vs. constant-pressure ideal cycles • When, in each cycle, the fuel is introduced and ignited

💭 Think About

• First, recall what is assumed about the combustion process in the ideal Otto cycle. Is it at mostly constant pressure or mostly constant volume? • Next, recall how the ideal Diesel cycle combustion is modeled. What is held approximately constant during the main combustion phase? • Think about when the fuel is injected in a Diesel compared with an Otto (spark‑ignition) engine. How does that affect how much fuel is present at the moment of ignition?

✅ Before You Answer

• Verify which cycle assumes constant-volume heat addition and which assumes mainly constant-pressure heat addition. • Check which choice, if any, describes a behavior that is unique to the Otto cycle’s ideal combustion model and not used in the Diesel model. • Confirm which engine type has the entire fuel charge already in the cylinder before ignition and which introduces fuel during the combustion event.