Carburetor air-fuel ratio calculations
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This document discusses calculations of air-fuel ratios in carburators. It first describes the basic components and airflow in a simple carburator. It then presents equations for determining the theoretical mass airflow rates of both air and fuel through the carburator, taking into account factors like compressibility of air, pressure differences, temperatures and densities. The document concludes that the air-fuel ratio depends on factors like the venturi throat diameter, fuel jet diameter, pressure difference across the venturi and densities of air and fuel. It also provides an example problem solving for the air-fuel ratio of a carburator with given specifications under two conditions, neglecting and accounting for the fuel nozzle tip.
![PROBLEM !!!
The venturi of a simple carburettor has a throat diameter
of 20 mm and the coefficient of flow is 0.8. The fuel orifice
has a diameter of 1.14 mm and the coefficient of flow is
0.65. The gasoline surface is 5 mm below the throat.
Calculate
(i) The Air fuel ratio for a pressure drop of 0.08 bar when
the nozzle tip is neglected [CHECK SOLUTION A/F
=15.15:1 ]
(ii)The air fuel ratio when the nozzle tip is taken into
account. [CHECK SOLUTION A/F =15.19:1]
Assume Density of air and fuel as 1.2 Kg/m3 and 750
Kg/m3](https://image.slidesharecdn.com/2-carburetorair-fuelratiocalculations-210520170443/85/Carburetor-air-fuel-ratio-calculations-19-320.jpg)
Carburetor air-fuel ratio calculations
- 1. CARBURETTOR AIR FUEL RATIO CALCULATIONS UNIT-2 EME-505 I.C.ENGINES AND COMPRESSORS (2013 batch) BY V.K.YADAV MECHANICAL ENGG. DEPTT G.L.B.I.T.M 20-May-21
- 3. CARBURETTOR A/F DETERMINATION Can you write STEADY FLOW ENERGY EQUATION (SFEE) ?????? for section A-A and B-B 20-May-21
- 4. AIR-FUEL RATIO CALCULATIONS Exact analysis (Practical case ) q-w = (h2-h1) + (C2 2-C1 2)/2 If we take compressibility of air into account, the air flow rate will change (but the fuel flow rate will remain same as it is incompressible) z
- 5. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21
- 6. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21 So the C2 expression will become
- 7. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21 As P1 v1 ᵧ = P2 v2 ᵧ V1 is specific volume = 1/rho
- 8. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21
- 9. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21 Eq. C.1 Theoretical mass flow rate
- 10. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21 C.1
- 11. AIR-FUEL RATIO CALCULATIONS Contd.. 20-May-21 Note that due to petrol surface being lower than the top of the jet by z meter , the Pressure difference becomes (P1-P2-zgρf) Instead of (P1-P2)
- 12. 20-May-21 AIR-FUEL RATIO CALCULATIONS Contd..
- 13. 20-May-21 AIR-FUEL RATIO CALCULATIONS Contd.. Note: To Calculate the exact air flow, in addition to pressure drop, initial pressure P1 and initial temperature T1 are required The compressibility of air is small for the velocities encountered. For a throat air Velocity of 75 m/s and a corresponding pressure difference of 25 mm of Hg, the air Fuel ratio, as calculated neglecting compressibility would require a correction of about 1.5% to increase the richness. Size of the Carburettor: The size of the carburettor is generally given in terms of diameter of throat in mm, and jet size in hundredths of a mm, i.e. jet no 50 has diameter of 50/100 mm. - The size of venturi throat is about 30-35 mm. The jet diameter is about 1/16 of Venturi Diameter - (P1-P2) is about 50 mm Hg - Velocity at throat is about 90-100 m/s - The coefficient Cda is usually 0.85
- 14. 20-May-21 AIR-FUEL RATIO DETERMINATION neglecting compressibility of air (Case II) Approximate analysis (Assuming constant density of air) Assuming initial velocity of air as negligible C1
- 15. 20-May-21 AIR-FUEL RATIO DETERMINATION neglecting compressibility of air Contd…
- 16. 20-May-21 AIR-FUEL RATIO DETERMINATION CONCLUSIONS REGARDING A/F RATIO From the expression of mass flow rate that we’ve derived it can be observed that
- 17. 20-May-21 AIR-FUEL RATIO DETERMINATION CONCLUSIONS REGARDING A/F RATIO Contd.. From the expression of mass flow rate that we’ve derived it can be observed that
- 18. 20-May-21 AIR-FUEL RATIO DETERMINATION CONCLUSIONS REGARDING A/F RATIO Contd.. From the expression of mass flow rate that we’ve derived it can be observed that
- 19. PROBLEM !!! The venturi of a simple carburettor has a throat diameter of 20 mm and the coefficient of flow is 0.8. The fuel orifice has a diameter of 1.14 mm and the coefficient of flow is 0.65. The gasoline surface is 5 mm below the throat. Calculate (i) The Air fuel ratio for a pressure drop of 0.08 bar when the nozzle tip is neglected [CHECK SOLUTION A/F =15.15:1 ] (ii)The air fuel ratio when the nozzle tip is taken into account. [CHECK SOLUTION A/F =15.19:1] Assume Density of air and fuel as 1.2 Kg/m3 and 750 Kg/m3