Yes, the fuel injection timing affects the in-cylinder temperature and its distribution. Since NOx formation depends on temperature level and time that this temperature lasts, the injection timing also affects the NOx formation.

More information about fuel injection timing may be found in the book "Internal Combustion Engine Fundamentals" by John B. Heywood.

Sincerely.

Injection timing is the time span between the start of injection and the TDC of the engine piston. Injection timing has a strong influence on injection pressure, combustion process, and practically all engine emissions. Injection duration is the time span from the beginning to the end of injection. In general, injection duration should be as short as possible. At higher engine speeds, injection duration should become longer and the mean injection pressure should be reduced Injection rate represents the quantity of fuel injected per unit of time into the combustion chamber. Variations of injection rate history influence mixture preparation, combustion process, and harmful emissions. Injection timing depends to a great extent on fuel properties and on geometrical parameters of the pump, high pressure tube, and injector.

Early injection timing leads to longer ignition delay which results in accumulation of large amount of evaporated fuel before the start of combustion. Longer ignition delay is due to lower values of pressure and temperature inside the cylinder during the initial period of fuel injection at advanced injection timings. The longer ignition delay leads to rapid burning rate and the pressure and temperature inside the cylinder rises suddenly. The shorter ignition delay is due to pressure and temperature inside the cylinder during the initial period of fuel injection being high. The shorter ignition delay shortens the mixing time, which leads to slow burning rate and slow rise in pressure and temperature. The NOx emission increases with early injection timing. It has been proved that the use of early injection provides lower soot and higher NOx emissions than the late injection.

Yes, it will affect the temperature and the NOx formation, but the effect will be different from that in a CI engine, because in GDI, injection is caused by the spark, rather than by auto-ignition. Given below is what is a likely scenario...

Assuming the spark timing remains constant, the major influence of injection timing will be on the air-fuel mixture distribution. With very advanced timing, it will be more homogeneous everywhere, while the stratification will increase upon retarding the timing, most probably resulting in richer mixtures near the spark plug. The NOx formation in a spark ignition engine peaks for slightly lean mixtures - for equivalence ratio (phi) between 0.9 to 1. Therefore, whichever injection strategy maximises the occurrence of this band of equivalence ratios is likely to result in more NOx. In other words, the mean equivalence ratio will be around 0.9 - 1.0 for this timing. This timing will depend on the overall equivalence ratio. Assuming the overall equivalence ratio is 0.9, advancing the injection, will give more NOx, as it will provide better homogenisation with most of the mixture at the the equivalence ratio of 0.9. If the overall equivalence ratio is 0.3 say, a relatively retarded timing will give more NOx, because early injection causes over-leaning and less NOx, while late injection will result in zones where the equivalence ratio lies in the range 0.9 to 1.

Dear friend, timing is everything.

Nox is a function of local air availability (oxygen) and in-cylinder temperature both.

Local Oxygen Availability depends on mixing extent and relative air (lean or rich).

There is the reason why the Nox peak for the SI engine is found at slightly rich operation. Although SI working in homogeneous mode has uniform local air availability, the flame temperature also contributes to Nox, at rich condition less oxygen but flame temperature accelerates kinetics to produce an overall peak at slightly rich.

Now in GDI, injection timing controls mixing as well as charge temperature.

Charge temperature is lowered due to fuel vaporization. The extent to which the heat for vaporization derived from bulk charge depends on injection timing.

Suppose too early injection timing results in a high piston and wall impingement that results in vaporization of charge from cylinder component, not from bulk charge. Early intake valve closing (EIVC) sometimes helps to cope up with too early injection timing using accelerated flow due to small lift and duration. But, it shortens the injection duration window, which means any injection beyond the valve closing time results in high penetration and high film formation on wall and piston due to lack of intake flow momentum due to downwards moving piston expanding closed intake charge. So an effective solution would be use low injection duration with EIVC if more is needed to increase injection pressure, not duration.

A little delay of injection towards BDC minimizes wall and piston film with late intake valve close (LIVC), hence lower charge temperature, lower Nox probability.

We can't say absolutely still, because we don't know the relative air. In order to improve mixing, we can use a modified port to create tumble motion to accelerate the mixing process, to provide uniform distribution. In the case of multi-valve (4 valve i.e. 2 intake and 2 exhaust), we can use the valve deactivation method for low BMEP to create swirl or tumble dominated flow to target better mixing.

Remember till, now we are talking about Homogenous DI (Induction Stroke), injection timing, after making sure proper mixing, in order to control we need to target cylinder TDC temperature, although evaporative cooling minimizes TDC temperature, the adiabatic flame temperature depends on fuel concentration.

A too large amount of fuel results in fuel entrainment case, lower Nox, temperature are high but oxygen limits Nox amounts.

A too large amount of air results in air entrainment case, lower Nox, here overall temperature decreases, due to the high thermal capacity of charge.

SI Nox curve is the best example.

Keep injection pressure constant (Although literature suggest induction mode injection done at 60 bar and stratified injection at 100-150 bar)

Coming to stratified mode, injection timing is during the compression stroke, lower scatter (cone angle) and penetration, fuel stay in forms of droplets at point of ignition. Here dispersion of fuel droplet in the cylinder is dominated by in-cylinder pressure.

Hence, in stratified mode, there is a high chance of a high local fuel-rich spot. Therefore Nox formation in most cases is in-cylinder temperature dominated, kinetically speaking, but here one another parameter that clouds oxygen availability is atomization of the spray. Atomization is more important than oxygen availability because stratified operate by default at the lean conditions. But in extreme operation condition oxygen comes into the picture. In cases of retarded ignition, fuel is provided with a relatively greater duration of time to vaporize and mix, then Nox will be limited by local oxygen availability.

In the end:

Keep in mind mixing in induction stroke for homogenous mode is dominated by intake flow momentum, while in the compression stroke for stratified mode, mixing is in-cylinder pressure dominated due to compression.