Reaction stu dies can be very helpful towar d un der- stan ding th e mechan isms an d int er-relations of operat - ing an d design param eters, espe cially when combined with math emat ical modeling of th e tran sient part iculat e filter operat ion。 Such an app roach ha s bee n recent ly prese nt ed by th e auth ors in a pur ely modeling stu dy, using li teratur e data to describe th e rat e laws。17 The prese nt work aims at exploiting expe rimenta l data an d math emat ical modeling, towar d bett er un derstan ding, an d describing th e NO2-soot reaction phenomena un der real-world diesel engine operat ing conditions。

Exp eri men tal Setup : Tes t Protoco l

The expe riment s were carr ied out on an engine bench, using a  diesel  engine  equipped with an  oxidat ion cata lyst an d a part iculat e filter in series。 Figur e 1 shows schemat ically th e expe rimenta l layout 。

The engine displacement is 1。9 L。 It is a direct- injection, tur bochar ged, an d int ercooled engine with exhau st gas recirculat ion (EGR)。 The basic engine specificat ions ar e give n in Table 1。 Furth er deta ils on th e engine can  be foun d in ref  18。

The oxidation cata lyst is th e original part aged at real driving conditions for app roximat ely 20 000 km 。 Its geometr ical data ar e give n in Table 2。 This cata lyst is mount ed at th e exhau st pipe 0。70 m downstr eam of th e tur bochar ger。 It ha s to be ment ioned that th e oxidat ion cata lyst used in th is stu dy is not optimized for NO2 production becau se th e manu factur er’s tar get was th e eliminat ion of CO an d HC emissions。  The cordierite part iculat e filter is insta lled directly downstr eam of th e

10。1021 /ie020379 t  CCC: $22 。00 © 2002  American  Chemical Society Pu blis hed on  Web 09/20/2002

Figu re 1。 Experimenta l layout: T, temperatur e th ermocouple; P, press ur e tran sd ucer。

Tab le 1。  Diese l  Eng ine  Speci ficatio ns

manu factur er Volks wagen

engine type direct injection, tur bochar ged, int ercooled

cylinders four , in line

displacement 1896 cm3

compressi on rat io 19。5:1

injection system type Bosch VP 34

rat ed power 66  kW at  4000 rpm

rat ed torque 182 Nm  at 2300  rpm

Tab le 2。  Geome trical  Data  of the  Oxidation   Cata lyst

cata lyst diam eter (mm) 130

cata lyst length (mm) 100

chann el density (cells /in。2) 400

wall th ickn ess (mm) 0。15

Tab le 3。 Geome trical Data and The rmophys ical Prope rti es of the P arti cu late  Fi lt er

filter mat erial cordierite

cell density (cells /in。2) 100

wall th ickn ess (mm) 0。43

diam eter (mm) 144

length (mm) 152

plug length (mm) 10

subs trat e perm eability (m2) 4 × 10-3

subs trat e density (kg/m3) 1600

oxidation cata lyst。 The geometrical an d th ermophysical propert ies of th e filter ar e give n  in Table 3。