Power system (fuel system). The main differences between gasoline and diesel engines

4.11.9 Full load 

At full engine load, the air-fuel mixture, which is supplied to its cylinders must be enriched. This is essential for obtaining the maximum power from the engine. The simple carburetor does not provide such level of enrichment. A special device, which is called an economizer, must be installed into the carburetor in order to fulfill this requirement.

When the throttle blade is opened quickly (when pressing the accelerator pedal), more gas must be supplied, enriching the mixture so that the engine quickly increases the number of revolutions, increasing power.

In case if the throttle blade is quickly opened in the simple carburetor, at the first moment, a strong dilution of the mixture is obtained. As a result of this the speed of acceleration (acceleration capability) of the engine deteriorates. This is explained by the fact that air, which has a lower density and has good mobility, when opening the shutter immediately rushes into the mixing chamber in a significant amount. Due to its higher density, the fuel is less mobile and does not have time to pass quickly through the orifice plug at the first moment. Therefore, the mixture becomes diluted. In order to increase the acceleration capability of the engine, a special device, which is called an accelerating pump, is installed into the carburetor.

Примечание
Thus, the simple carburetor under various operating conditions of the engine does not provide its power supply with an air-fuel mixture of the proper composition and must be equipped with additional devices: to compensate the mixture, for easy starting of the engine, for its idle run, for enriching the mixture at full load and for improving the acceleration capability of the engine (Figure 4.48).

Figure 4.48 Carburetor of VAZ 2108/2109 “Solex” car family.

1. Acceleration pump actuator arm; 
2. Starting arrangement diaphragm adjustment screw;
3. Starting arrangement diaphragm;
4. Starting arrangement air duct; 
5. Solenoid shut-off valve; 
6. Idle system fuel orifice plug; 
7. First chamber main air bleed; 
8. Idle system main air bleed; 
9. Air shutter; 
10. First chamber main dosing system disperser; 
11. Accelerator pump disperser with ball valve; 
12. Second chamber main dosing system disperser; 
13. Econostat disperser; 
14. Second chamber main air bleed; 
15. Second chamber transition air bleed; 
16. Float chamber balancing channel; 
17. Float chamber; 
18.  Fuel (needle) valve; 
19. Fuel return orifice connection; 
20. Mesh filter; 
21. Fuel supply connection hose; 
22. Diaphragm of economizer of power modes; 
23. Economizer fuel jet of power modes; 
24. Ball valve of economizer of power modes; 
25. Float; 
26. Fuel jet of econostat with tube; 
27. Second chamber transition fuel jet with tube; 
28. Second chamber emulsion tube; 
29. Second chamber main fuel jet; 
30. Outlet of the second chamber transition system; 
31. Throttle blades; 
32. Damping orifice plug; 
33. Throttle blades;
34. First chamber transition system slot; 
35.  Outlet of idle run system; 
36. Carburetor heating unit; 
37. Adjustment screw of “quality” composition of the idle system mixture; 
38. Engine breather system connection hose; 
39. Unloading unit connection hose to the vacuum regulator of the ignition distributor; 
40. Exhaust gas system recirculation unloading unit connection hose; 
41. First chamber main fuel jet; 
42. First chamber emulsion tube;
43.  Acceleration pump ball valve; 
44. Acceleration pump diaphragm; 
45. Acceleration pump push rod.