Study On The Emission In A SI Engine With Secondary Air During Cold Start

Nowadays, vehicle production growing makes life easily more, however, its emission not only become a worse resource in environment pollution, but also threaten to human's health. As a result, serve regulations are implemented worldwide in order to reduce vehicle emission and protect environment around us. Euroâ…£regulation takes lower emission limits and require a new test driving cycles as well, namely taking emission measurement in the first 40s after start. During FTP and ECE-EUDC test driving cycles, approximately 60%-80% unburned HC and CO are generated in SI engine. What's worse, catalyst is almost useless at this time because of lower working temperature, so that, numerous pullouts exhaust to environment without any treated. As an effective after-treatment, secondary air can reduce emission during cold start, by that way, post oxidation reduce the raw engine pullouts before catalyst which is heating the catalytic substrate faster at the same time.So that, this paper gives an emphasis on secondary air influencing in an SI engine's emission during cold start based on a series of cold/warm starting experiments including a Secondary Air System application in 4G10 engine, experiment data testing/recording, experiment result calculating /analyzing and so on. Main work in this literature includes:1) A Secondary Air System is designed and implemented in exhaust system of TOYOTA 4G10 engine;2) A active secondary air supply system is designed including air pump, air canister and electronic valve used for adjusting differential air mass flow, which is benefit for steady secondary air flow as well as simple injection operation;3) High-speed data acquisition and reliable data storage are achieved by means of high-performance PCI-1710 card; 4) Emission data are acquitted and stored in computer through a series connecting procedures by means of AVL gas analyst;5) Emission experiment data are transferred from volume percentage to volume flow rate in order to exposed exhaust rule scenically;6) Investigate on secondary air influence in exhaust temperature and pullouts with different air mass flow thorough cold and warm start experiment separately under controlling initial cooling water.Experiment results show that:1) Unburned HC and CO are reduced dramatically in SI engine during start process with Secondary Air System;2) On the condition of cold start, unburned HC and CO are reduced due to massive oxygen produced from secondary air system, which is needed in post oxidation, they are decreased by 19% and 27% separately compared with original emission simultaneously, time for catalyst light-off is also shorted(50% conversion efficiency);3) Different result comes out from different secondary air mass flow. Smallness cause to lack of oxygen needed by post oxidation, on the contrary, majority lead to cool off exhaust gas which is not benefit for exothermic reaction too;4) On the condition of warm start, emission conversion efficiency is not affected obviously by secondary air., HC emission is different from original engine with secondary air, including: peak is decreased by 55% ,so as to stabilization value in 5 seconds after start, but there is no different between different secondary air flow. CO emission is reduced greatly in peak by 86% and 88% separately, between the front and back with secondary air. High conversion efficiency of CO has happened at the beginning of the whole start process, which indicates that temperature is an indispensable factor in thermal oxidation reaction, however, its conversion efficiency is lower during catalytic oxidation process which is just about 10%.It is observed that no difference between different secondary air flow in reducing CO emission.5) Different strategy should be used to control secondary air after concluded from the result of cold/warm start experiment, for example, time for secondary air action should be shorted under warm start condition.