🔍 Key Concepts

• Air-fuel mixture in internal combustion engines • Difference between weight (mass) and volume measurements • Which stroke of the 4-stroke cycle is typically associated with defining mixture ratios

💭 Think About

• Is air/fuel mixture usually discussed in terms of how many pounds/kilograms of air to how many pounds/kilograms of fuel, or in terms of their volumes? • When textbooks give a "stoichiometric" air/fuel ratio (for example, about 14.7:1 for gasoline), are they usually referring to weight or volume? • In a four-stroke engine cycle (intake, compression, power, exhaust), during which stroke is the quantity of fuel relative to air practically defined or metered for combustion?

✅ Before You Answer

• Decide first whether air/fuel ratio is based on weight or volume—eliminate all choices using the wrong basis. • Decide second whether the ratio is tied to the compression stroke or the power stroke—eliminate those using the less appropriate stroke. • Confirm that the remaining option clearly matches how engineering references define air/fuel ratio.