To reduce NOx concentration in exhaust to a specified low level.
A specified quantity of moisture 14 is added to fuel oil 12 by an emulsifying device 16 coping with the seasonally changing moisture quantity contained in charged air. A reducing device 10 for reducing NOx in exhaust with NH3 is provided in an exhaust pipe 3 system. A computer 7 obtains the function value KO by substituting various parameter values at the time of delivery in a dominant expression K of NOx concentration which is the function of absolute humidity X of charged air, temperature Tb of changed air, and specific gravity γ and nitrogen content(y) of fuel, multiplies the obtained function value by the NOx regulation value CO* at the time of delivery adjustment and divides it by the first regulation value C1* to obtain the function value Ks at the time of operation, computes the added moisture quantity X* required to make NOx concentration in exhaust the first regulation value as well as to make the function value obtained by substituting various parameters at the time of operation in the dominant expression K, the function value Ks at the time of operation, computes the water added quantity Y proportional to engine output L and the difference (X*-X) between the computed moisture quantity and the moisture conversion value of atmospheric absolute humidity at the time of operation obtained by measurement or the like, and outputs a signal indicating the computed water added quantity Y to the emulsifying device.
YAMADA TETSUTSUGU
TANABE KENJI
