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Notes and summary: carburettor

Short answer

A carburettor uses a venturi to draw petrol from a jet, with a float chamber maintaining fuel level. A compensating jet prevents over-rich mixture at high speed, and an idler jet supplies a richer mixture for starting and idling when the throttle is nearly closed.

After taking notes, write a summary of the following passage. Since it is essential to secure rapid and complete combustion in the cylinder of an internal combustion engine, the fuel and air mixture must be thoroughly mixed; and further, it must be in the correct proportions for all running conditions of the engine. [passage of about 480 words on the working of a carburettor: jet, venturi, float chamber, throttle valve, compensating jet and idler jet] ... This jet will only function when the throttle is nearly closed. When it is opened for faster running, the suction round the edge of the throttle decreases, and the idler automatically ceases to act.

Notes

Title: Working of a carburettor

  1. Purpose: for rapid, complete combustion, fuel and air must be well mixed in correct proportions for all running conditions
  2. Simple carburettor
    • Air passes through a venturi (narrow throat) in the intake manifold; pressure falls
    • Suction draws petrol from a jet and sprays it into the air
    • Float chamber (float and needle valve) keeps petrol level constant
    • Throttle valve (controlled by accelerator pedal) regulates amount of mixture
  3. Problems of single jet
    • At high speed, petrol drawn rises faster than air flow, so the mixture becomes too rich
  4. Compensating jet
    • Second jet fed from a well open to the atmosphere
    • Supplies petrol quickly at first, then less as the well empties; main jet gives more as speed rises
  5. Starting / idling
    • Throttle almost closed: suction at main jet too low
    • Idler jet near throttle valve works only when throttle is nearly closed; stops when throttle opens

Summary

A carburettor mixes petrol and air in the correct proportions for combustion. Air flows through a venturi, where reduced pressure draws petrol from a jet fed from a float chamber, and a throttle valve controls the amount of mixture. A single jet gives a mixture that becomes too rich at high speed, so a compensating jet fed from a well is added to keep the mixture correct. For starting and slow running, when the throttle is almost closed, an idler jet near the throttle valve supplies the richer mixture and stops acting when the throttle is opened.

(About 110 words.)

✓ Answer checked by Claude Opus 5.5 (high effort)

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