Contents: Formation of the fuel mixture and…⇓ Engine Criteria ⇓ Fuel injection timing ⇓ Fuel atomization ⇓
Formation of the fuel mixture and combustion process
- injection pressure;
- injection time;
- aerosol spread (nozzle number, spray profile, spray direction);
- fuel injection timing;
- air movement;
- amount of air.
These factors affect the engine's emissions of harmful substances and fuel consumption. High combustion temperatures and high oxygen levels lead to increased NOx formation. Soot emissions increase with reduced air supply and poor fuel mixture formation.
Engine Criteria
The configuration of the combustion chamber and air intake duct can have a positive effect on reducing exhaust emissions. If the air movement in the combustion chamber is carefully coordinated with the fuel jets and atomizers, which promotes efficient mixing of air and fuel, complete combustion of the injected fuel is achieved. In addition, positive effects are achieved by homogenizing the mixture of air and exhaust gas cooled in the EGR tract. The use of four valves per cylinder and a turbocharger with a variable geometry turbine (VTG) also helps reduce exhaust toxicity and increase specific power.
Fuel injection timing
Reducing combustion temperatures and slowing down the fuel injection process leads to a reduction in NOx content in the exhaust gases. However, if these parameters are significantly reduced, the HC content in the exhaust gases and fuel consumption increase, as well as soot emission under high engine loads.
If the fuel injection timing deviates by only 1° (crankshaft) from the optimum value, the NOx content can increase by 5%, taking into account that a deviation of 2° (crankshaft) in the direction of advancing the injection moment can lead to an increase in pressure in the engine cylinders up to 10 bar, and a deviation of 2° (crankshaft) in the direction of delay can increase the exhaust gas temperature by 20°. Such high sensitivity requires extreme precision in adjusting fuel injection timing.
Fuel atomization
Fine atomization of fuel promotes efficient mixing of air and fuel. This makes a significant contribution to reducing soot and HC emissions. High injection pressure and optimal geometric configuration of the nozzle hole result in good fuel atomization.
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To avoid the appearance of visible soot emissions, the amount of fuel injected must be limited in accordance with the amount of air entering the engine. This requires an excess air supply of at least 10...40% (X =1.1...1.4). After the nozzle needle is closed, the fuel remaining in the nozzle hole evaporates and leads to an increase in HC emissions. This means that such harmful volumes must be minimized.