Fuel mixture formation and combustion process
- injection pressure;
- injection time;
- aerosol spread (No. of atomizer, spray jet profile, spray jet direction);
- the moment of fuel injection;
- air movement;
- the amount of air.
These factors affect engine emissions and fuel consumption. High combustion temperatures and high levels of oxygen concentration result in increased NOx formation. Soot emission increases with a decrease in the amount of air and insufficient formation of the fuel mixture.
Engine Criteria
The configuration of the combustion chamber and air intake duct can positively influence the reduction of exhaust gas emissions. If the movement of air 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, the positive effects of homogenizing the mixture of air and exhaust gas cooled in the EGR path are achieved. The use of four valves per cylinder and a turbocharger with a variable geometry turbine (VTG) also helps to reduce the toxicity of exhaust gases and increase power density.
Fuel injection timing
Reducing the combustion temperature and slowing down the fuel injection process leads to a decrease in the NOx content in the exhaust gases. However, if these parameters are significantly reduced, the content of HC in the exhaust gases and fuel consumption increase, as well as the emission of soot at high engine loads.
If the fuel injection timing deviates by only 1° (crankshaft) from the optimal 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, it can increase the temperature of the exhaust gases by 20°. This high sensitivity requires extreme precision when adjusting the fuel injection timing.
Fuel spray
Fine atomization of fuel promotes effective mixing of air and fuel. This contributes significantly to the reduction of soot and HC emissions. The high injection pressure and the optimum geometry of the atomizer opening result in good fuel atomization.
To avoid visible soot emission, 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 closing the atomizer needle, the fuel remaining in the atomizer hole evaporates and leads to an increase in HC emission. This means that such harmful volumes should be kept to a minimum.