Chapter 3. Fueling Considerations.|
13318 words. 22 illustrations.
The Fuel Consumption Loop. Plotting from rich to weak. Best power fuel requirement. Best economy fuel requirement. Stoichiometric. Plotting part load loops against manifold pressure or torque. Fueling specification for production engines. Adaptive memory. Self mapping.
Specific Consumption. The specific fuel consumption map. Contours of specific consumption. Best speed and load conditions. Significance of piston speed. Specific air consumption.
Losses and Improvements. Different speeds for peak torque and peak volumetric efficiency. Throttling losses. Inlet valve throttling reduces losses. Effects of various factors. Air temperature. Gearing. Lean burn. Cylinder disablement. Fallacy of need for high vacuum. Ideal acceleration. Compression ratio. Specific fuel consumption possibilities.
Exhaust Gas Analysis. Relationship of fuel consumption, torque, emissions. Mechanism of NOx formation and reduction in three way catalyst. Reason for stoichiometric fueling.
Lambda Feedback. The Zirconia Lambda sensor. Construction and operation. Factors governing sensitivity and deterioration. Heated types. ECU response techniques. Biasing response. Planar type. Titania type. Wideband Zirconia sensor. Broadband Zirconia sensor. Monitoring efficiency. OBD2 requirement for 2nd sensor.
More about Air/Fuel Ratio and Exhaust Gases. Understanding the balance between raw CO, CO2 and O2 with changing air/fuel ratios as a guide to diagnosis. Air injection. Catalyst light-off.
Effect of Compression Ratio on Fueling Limits. Higher compression extends air/fuel ratio tolerance. Variable compression unthrottled operation.
Finer Details about Fueling. Idle fueling - richness preferred. Cold start and warm up. Controlling emissions during cold start and warm up. Transient conditions - acceleration and deceleration. Icing problems - not just carburettors.
Injection Qualities -Timing, etc. Properties of early mechanical systems - continuous flow, timed squirts, upstream, downstream. Vague cycle match of Bosch D Jetronic. Grouped twin shot. Sequential and part sequential. OBD2 connection.
Mixture Preparation. Need for the fuel to be vapourised (evaporated). Benefits of raised temperatures and fine atomisation. Shell Vapipe. The Hedgehog. Sonic carburetors. Increased fuel pressure. Different needs for high speed racing engines and for production engine emission control. Air assisted injection.
Direct Injection. Hesselman engine. German WW2 aircraft engines. Mercedes and Ferrari race engines. Ricardo supercharged two stroke. High pressure multi-spray injectors. Air charge movement. Internal charge cooling. Heated injectors. Piezo injectors. Multi-fuel application.