Nor mally, cyl in der pres sure was used as a cri te rion of com bus tion oc cur rence, while in some con di tions, it may be un re li able when iden ti fy ing lean mix ture combus tion. This is par tic u larly im por tant for fu els like liq ue fied pe tro leum gas, which has good ca pac ity for lean com bus tion. In this study, a fast re sponse NO de tec tor, based on the chemiluminescence method, was used to mea sure real time NO emissions in or der to eval u ate the tech nique as a cri te rion for es tab lish ing com bus tion oc cur rence. Test re sults show that real time NO emis sions can be used to iden tify the cyl in der com bus tion and mis fire oc cur rence dur ing en gine crank ing, and real time NO emis sions can be used to un der stand the com bus tion and mis fire oc currence. Real time NO emis sions mostly hap pened in first sev eral cy cles dur ing cold start, and NO emis sions in creased with the spark tim ing ad vanc ing.
In tro duc tionNowdays, de mands for emis sion re duc tion of the ve hi cle be came very ur gent which lead to stricter emis sion reg u la tion. The cold start emis sion at -7 °C en vi ron men tal tem per a ture was re quired in the Eu rope and the USA emis sion reg u la tion [1]. The re search shows that 50%~80% HC and CO emis sions was pro duced dur ing the cold start [2, 3]. Since the 1990s, many re searches about HC emis sions dur ing the cold start were car ried out of China. Re cently, the sim i lar re search was car ried on in China. Pro fes sor Huang [4,5] etc. stud ied the HC emissions and their in flu enc ing fac tors dur ing cold start. Yong [3, 6] etc., com bined with study of the light off char ac ter is tic of the three-way-cat a lytic con verter, stud ied the emis sions and af fect ing fac tors dur ing cold start and warm-up.Those stud ies show that the ex cess air co ef fi cient was the key pa ram e ter for the first fir ing cy cle (FFC) dur ing cold start. The mix ture con cen tra tion be ing too rich or too lean will increase the HC emis sions of the FFC dur ing cold start sharply. There fore, the main ob ject was to op ti mize the ex cess air co ef fi cient in the FFC dur ing cold start. HC emis sions were one of the judg ments for the op ti mum mix ture con cen tra tion. While, study of HC emis sions were not Zu, Y., et al.: Cold Start Characteristics Study Based on Real Time NO Emissions in .