Study On Combustion And Emissions Characteristics Of A Hydrogen Fueled Internal Combustion Engine Under Cold Start Conditions

During the operation of hydrogen fueled internal combustion engine?H₂ICE?,especially under high load conditions,a large number of NOx emissions will be generated,which has become a bottleneck hindering their commercial application.Although domestic and foreign scholars have made extensive research on the emissions control of NOx in the H₂ICE,these studies mainly focus on the combustion and emissions characteristics of H₂ICE under idle,partial load and high load conditions.There are few reports on the combustion and emissions characteristics of H₂ICE under cold start conditions.The lower in-cylinder temperature causes less NOx formation under cold start conditions,but at the same time,the post-processing system has not reached the working temperature,which makes the harmful emissions directly discharged into the atmosphere.The emissions of H₂ICE under cold start conditions is not optimistic.Therefore,exploring the combustion and emissions characteristics of H₂ICE under cold start conditions,seeking a simple and efficient NOx control technology for cold start conditions is of great significance for improving the overall performance of hydrogen internal combustion engines and promoting hydrogen internal combustion engines.Therefore,in this paper,the combustion and emissions characteristics of a H₂ICE were analyzed at different excess air ratio???and ignition timing to realize a low NOx emissions level under the cold start conditions.Firstly,based on CHEMKIN simulation software,the initial temperature and pressure are 298 K and 0.1 MPa respectively,and the equivalence ratios are 0.6,0.8,1.0,1.2 and 1.4 respectively.The effects of different equivalence ratios on the laminar flame characteristics,active radicals and NO formation are analyzed emphatically.The results show that the rich hydrogen combustion strategy has a significant effect on inhibiting combustion temperature and reducing the formation rate of intermediate free radicals and NO.This part of work provides theoretical support for the experiment.In this paper,a four-cylinder multi-point electric injection ignition internal combustion engine produced by Beijing Hyundai Motor company was used as the prototype,which was transformed into a PFI hydrogen fueled internal combustion engine,and a set of self-developed electronic control unit was used to control the ignition timing and the hydrogen injection pulse width.By changing the pulse width of hydrogen injection and ignition advance angle,the parameters such as excess air ratio of mixture and ignition timing can be adjusted during cold start condition of the H₂ICE.Secondly,based on the test system of a H₂ICE,this paper conducted an experimental study on the combustion and emissions characteristics of the H₂ICE under cold start conditions with different excess air ratio,and focused on the influence of rich H₂ combustion strategy on the cold start performance and NOx emissions of the H₂ICE.The results show that the rich hydrogen combustion strategy can improve the cold start performance of the H₂ICE and reduce the NOx emissions during cold start.When the excess air ratio declines from 1.54 to 0.72,the successful starting time of engine is shortened by 20.8%,and the average NOx emissions of the engine is reduced by about84.3%in the first 6 seconds.At the same time,under the condition of rich hydrogen combustion,the higher in-cylinder temperature and engine speed during cold start is conducive to the evaporation of lubricating oil and the increase of HC and CO emissions,especially CO emission.Finally,aiming at the emissions of HC and CO during the cold start of the engine,the influence of ignition timing on the combustion and emissions characteristics of the H₂ICE under the cold start condition is studied in this paper.The results show that under the condition of?=0.7,when the ignition timing is gradually delayed from 25°CA BTDC to 10°CA ATDC,the successful starting time of the engine is firstly shortened and then extended,and the peak cylinder pressure rises first and then gradually decreases,while the average emissions of NOx,HC and CO decrease by 84.9%,33.6%and 23.8%respectively in the first 6 seconds under cold start conditions.It can be seen that under rich hydrogen combustion conditions,premature or late ignition is not conducive to cold start of the H₂ICE,and proper delay of ignition angle can effectively reduce NOx,HC and CO emissions during cold start of the H₂ICE.