高海拔下预喷策略对甲醇/柴油双燃料发动机燃烧与排放特性的影响

Effects of Pre-Injection Parameters on Combustion and Emissions of an Methanol/Diesel Dual Fuel Engine at High Altitude

通过搭建甲醇/柴油双燃料发动机专用试验台架,对某4缸高压共轨柴油机进气歧管改造加装喷醇器,系统地研究了2000 m海拔70%负荷下M0、M10、M15、M20甲醇替代率的预喷策略对双燃料发动机燃烧与排放特性的影响.结果表明:大气压力减小会导致滞燃期延长和缸内燃烧压力下降,甲醇替代率增加会导致滞燃期延长和缸内燃烧压力增大.采用预喷策略结合甲醇喷射,可以提高燃烧压力,降低常规与非常规排放.在最大转矩转速(1800 r/min)中高负荷(70%,321.3 N·m)下,相比纯柴油模式,20%甲醇替代率滞燃期延长44.76%,NO_(x)排放降低16.64%,CO和HC排放增加,并出现了甲醇和甲醛非常规排放.滞燃期与预喷正时呈非线性关系,过早或过晚预喷都会使滞燃期延长.各替代率下NO_(x)排放分别增加了4.77%、4.56%、6.89%、7.05%.增大预喷油量到4 mg,各替代率下滞燃期缩短了55.84%、43.46%、35.58%、23.21%,缸内燃烧压力明显增加,NO_(x)排放增加了4.76%、5.11%、6.74%、12.51%,CO和HC略有降低.甲醇/柴油双燃料模式下,合理调节甲醇替代率和预喷策略可有效控制滞燃期与减少排放.在该工况下,滞燃期、最大峰值压力、NO_(x)和CO随预喷参数变化趋势与平原低负荷工况一致,但在高海拔、高负荷条件下受预喷油量影响更明显,变化幅度更大.HC、CH_(3)OH排放趋势与平原低负荷不同.预喷策略改善了2000 m海拔下的燃烧恶化,减少了NO_(x)、CO、CH_(3)OH和CH_(2)O排放.通过预喷策略与甲醇替代率的协调控制可以减少高海拔下的滞燃期延长并减少高海拔下燃烧压力的降低,进而改善DMDF发动机的高原性能,达到减排的效果.

The intake manifold of a 4-cylinder high pressure common rail diesel engine was modified,an alcohol injector was installed,and a special test bench for methanol/diesel dual fuel engine was built.The influence of methanol substitution ratio(MSR)of M0,M10,M15 and M20 pre-injection strategy on combustion and emission characteristics of dual-fuel engine under 70%load at 2000 m altitude was sy stematically studied.The re-sults show that the decrease of atmospheric pressure leads to the prolongation of combustion delay period and the decrease of combustion pressure in cy linder,while the increase of methanol replacement rate leads to the prolon-gation of combustion delay period and the increase of combustion pressure in cylinder.Pre-injection stmategy combined with methanol injection can increase combustion presure and reduce conv entional and unconventional emissions.At the maximum torque speed(1800 r/min)and high load(70%,321.3 N·m),compared with the pure diesel mode,the ignition delay period of 20%methanol repl acement rate was 44.76%longer,NO_(x)emissions were 16.64%lower,C0 and HC emissions were increased,and methanol and forma Idehyde emissions were um-conventional.There is a nonlinear relationship between the ignition delay period and the timing of pre-injection.Premature or late pre-injection will prolong the ignition delay period.NO_(x)emissions increased by 4.77%,4.56%,6.89%and 7.05%at each replacement rate,respectively.When the pre-injection amount is increased to 4 mg,the ignition delay period is shortened by55.84%,43.46%,35.58%and23.21%,the combustion pres-sure in the eylinder increases obriously,NO_(x)emission increases by 4.76%,5.11%,6.74%and 12.51%,and.C0 and HC decrease slighty.In methano/diesel dual fuel mode,reasonable adjustment of methanol subtitution mte and pre-injection strategy can efectively control the ignition delay period and reduce emissions.Under this condition,the variation trend of ignition delay period,maximum peak pressure,NO_(x)and CO with pre-injection parameters is consistent with that under plain low load condition,but the influence of pre-injection amount and the variation nnge is more obvious under the condition of high-altitude and high load.HC and CH,OH emission trends are diferent from plain low load.The pre-injection strategy improved combustion detenioration at 2000 m.and reduced NO_(x),C0,CH_(3),OH and CH_(2)0 emissions.Through the coordinated control of pre-injection strategy and methanol replacement rate,the prolonged ignition delay period and combustion pressure eduction at high a titude can be reduced,and then the plateau performance of DMDF engine can be improved to achieve emission eduction efect.