Otto cycle fuel introduction — is external fuel injection required? State whether the following is correct: Engines working on the ideal Otto cycle do not require high-pressure fuel injection by an external source into the cylinder (mixture is prepared before admission).
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AYes
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BNo
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COnly for stratified-charge SI
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DOnly for carburetted engines
Answer
Correct Answer: Yes
Explanation
Introduction / Context:The ideal Otto cycle models a homogeneous, premixed charge that is compressed and then ignited by a spark. Historically, spark-ignition engines used carburettors to meter fuel upstream; modern SI uses port or direct injection but still does not rely on diesel-like high-pressure injection to trigger ignition.
Given Data / Assumptions:
- Otto cycle = constant-volume heat addition applied to a premixed homogeneous charge.
- Ignition source is a spark, not auto-ignition by compression.
- “External source injection” here refers to diesel-style high-pressure in-cylinder injection being essential for operation.
Concept / Approach:In the classical Otto framework, fuel is introduced and mixed with air before the intake valve, and the cylinder draws in the mixture. Thus, no high-pressure, in-cylinder “external” injection system is required to achieve combustion. While many modern SI engines use injection (port or DI) for mixture preparation and control, ignition still requires a spark and does not depend on compression ignition or mandatory diesel-type injection hardware.
Step-by-Step Solution:
Recall Otto assumptions: premixed, homogeneous charge at intake.Recognize spark ignition provides the heat addition at (approximately) constant volume near TDC.Conclude: diesel-like external high-pressure injection is not required by the ideal Otto concept → statement is correct.Verification / Alternative check:Carburetted engines fully satisfy the ideal Otto premise. Port-fuel-injected SI engines still premix before ignition; direct-injection SI times fuel delivery but relies on a spark, not compression-induced auto-ignition.
Why Other Options Are Wrong:
- No: Implies injection is required for Otto-cycle operation, which is not inherent.
- Conditional options: The ideal cycle definition is general and not limited to specific hardware era.
Common Pitfalls:Confusing “fuel injection present” with “fuel injection required for ignition.” SI uses a spark to initiate combustion; the presence of injectors does not change the fundamental ignition mode.
Final Answer:Yes