Visualization Research On Effect Of Hydrogen Blending On The Combustion Characteristics Of CNG-Diesel Dual Fuel Engine

CNG-diesel dual fuel combustion mode can not only take advantage of new energy sources,but also make full use of high compression ratio of diesel engine.It is a very feasible energy utilization mode.However,it suffers from the disadvantages of misfire and high HC emission in cold starting or light-load.This paper attempts to introduce hydrogen to improve its combustion characteristics.By adding natural gas hydrogen-donating(HCNG)supply system in the optical engine system,and combined with cylinder pressure acquisition system and high-speed photographic optical test technology to obtain the combustion pressure and combustion image in the cylinder,we study the effect of hydrogen belending on the heat release rate,ignition characteristics,combustion process,and temperature soot of CNG-diesel dual-fuel engine in different HCNG substitution ratios and main injectiom timing.The main conclusions are as follows:1)Based on the process of flame development and the heat release law,the CNG-diesel dual-fuel engine combustion process can be divided into four stages:(1)the retarding period,from the main injection time to the ignition time;(2)the ignition period,from the ignition time to cumulative heat release rate CA10 time;(3)fast burning period,from CA10 to CA60;(4)after-burning period,from CA60 to CA90.2)In all HCNG substitution rates,adding hydrogen(30%)can increase the peaks of cylinder pressure,pressure rise rate and heat release rate,shorten the ignition period and the fast burning period.However,at low and middle substitution rates,adding hydrogen delayes the peak phase and increased the retarding period.Only at high substitution hydrogen rate,the peak phases and the combustion characteristic point are obviously advanced with hydrogen addition,the retarding period,the post combustion period,combustion duration and the high temperature and high KL duration are shortened,the ignition area is increased,and the after-burning soot emission is reduced.It shows that at high HCNG substitution rate,the effect of hydrogen is more obvious.3)In all main injection timings,adding hydrogen(30%)can improve the peaks of cylinder pressure,the rate of pressure rise and the heat release rate,while the peak phase and ignition timing are advanced,the ignition period,fast burning period and combustion duration are shortened,the blue flame and yellow flame area are increased,the appear moments of early high temperature region and high KL factor region are advanced.However,the phase advance of the characteristic point increases first and then decreases with the main injection time,and the effect of hydrogen is more obvious when the main injection time is 10°CA BTDC.In the conditions of the high HCNG substitution ratio and the main injection time of0°CA BTDC,the peak values of cylinder pressure,pressure rise rate and heat release rate gradually increase,the peak phase advances,the ignition point and ignition area increase,and the retarding period shortens.Each feature point appears ahead.When the hydrogen addition ratio is higher than 20%,the flame duration can be obviously reduced,the average temperature and the average KL factor peak increase,the corresponding phase advance.