At low fuel-to-air equivalence ratios the NOX emissions
levels are negligible. With increasing , the combustion
temperatures increase, resulting in NOX formation. At a
threshold around 0:5 the NOX emissions increase
exponentially and reach their peak around 0:8.
Further increasing results in a decrease in NOX
emissions due to reduced availability of excess oxygen.
This trend is applicable with engines using homogeneous
mixture formation, employing qualitative load control.
With increasing load the fuel-to-air equivalence ratio
increases and NOX emissions follow the trend of Fig. 5.
This has implications for the load strategies used in
hydrogen vehicles, as will be explained in Section IV.