喷油时刻对缸内直喷汽油机颗粒物排放的影响

缸内直喷汽油机因其良好的节能性能,近几年来成为车用汽油机研究的重点,但也带来了颗粒物排放的问题.针对一款缸内直喷发动机,采用CFD数值模拟和发动机台架试验相结合的方法,研究了不同的喷射时刻对直喷汽油机混合气形成和颗粒物排放的影响.结果表明:缸内直喷汽油喷雾碰壁形成油膜与颗粒物排放有着直接的关系;在小负荷和中等负荷工况下,喷射时刻的优化能够有效地降低颗粒物数量排放.对于典型进气侧置喷油器缸内直喷汽油机,中小负荷工况优化的喷油策略为喷射时刻在进气冲程中期(约270,°,CA BTDC).     

乙醇DI/汽油PFI发动机性能与排放特性

基于一台点燃式发动机,对缸内直喷(DI)乙醇和进气道喷射(PFI)汽油的复合喷射方式进行了研究.与传统喷油模式相比,采用乙醇-汽油复合喷射能够提升发动机动力性.随直喷乙醇比例增加,缸内爆发压力升高;受乙醇燃烧速率和缸内冷却效果的综合影响,着火滞燃期和燃烧持续期先缩短后延长.最佳点火时刻下,单一汽油喷射(PFI和GDI)爆震频次超过10%,,发动机发生轻微爆震,而复合喷射乙醇比例超过20%,可消除爆震;随直喷乙醇比例增加,循环波动系数降低,当量燃油消耗率降低,指示热效率提高,复合喷射相对PFI可提高发动机热效率3.8%,;同时,能够有效降低NOx和HC常规气体排放物.通过采用相对较高的缸内直喷乙醇比例,复合喷射能够提高发动机热效率及抑制爆震并降低常规气体排放物.     

甲醇-汽油双燃料火花点火发动机试验研究

基于一台由缸内直喷汽油机改装而成的高压缩比双燃料汽油机,研究了甲醇-汽油双燃料喷射方式(M-G,是指进气道喷射甲醇,缸内直喷汽油)和汽油-甲醇双燃料喷射方式(G-M,是指进气道喷汽油,缸内直接喷甲醇)两种双燃料双喷方式对火花点火发动机燃烧排放特性、热效率和爆震抑制的影响。在试验过程中甲醇的喷射比例范围为0~100%。试验结果表明:相比于汽油单燃料发动机,两种双燃料喷射方式(M-G和G-M)都能够显著提高经济性、抑制爆震同时降低微粒排放;G-M双燃料喷射方式相比M-G双燃料喷射方式在抑制爆震、降低微粒排放上效果更加显著。     

基于并行计算的二次喷射式HCCI汽油机的三维数值模拟

建立了缸内直喷HCCI汽油机带进、排气道的燃烧系统的三维工作过程循环数值模型,实现了HCCI发动机包括进气、压缩、燃烧、膨胀和排气工作过程的三维循环模拟并进行了验证.首先基于并行计算进行了不同当量比(负荷)工况下HCCI发动机缸内过程的对比分析,研究了负荷对HCCI发动机着火、燃烧和排放的影响.进而模拟了缸内直喷二次喷射的HCCI发动机循环工作过程,解析了HCCI发动机着火燃烧和排放过程,揭示了HCCI发动机缸内直喷二次喷射控制着火的规律.计算结果有助于对HCCI燃烧过程的深入理解,为HCCI发动机燃烧过程的优化提供了依据.     

某GDI发动机二次喷油策略的试验研究

本文研究了某汽油机缸内直喷(Gasoline Direct Injection,GDI)发动机二次喷油策略对自然吸气直喷发动机燃烧性能、经济性和排放性的影响规律,优化了二次喷射比例和时刻,为该类型发动机相关参数优化提供了数据积累和依据.试验工况下,随着二次喷油比例的增加,燃烧质量变差,缸内爆发压力降低,缸内燃烧温度降低...     

直喷汽油对反应活性控制压燃负荷拓展影响的数值模拟研究

基于三维计算流体力学软件CONVERGE,通过数值模拟的方法,基于不同的燃油总量、直喷汽油量、预混汽油油量和汽柴油喷射时刻等参数,展开了缸内直喷汽油对反应活性控制压燃(RCCI)燃烧模式高负荷拓展影响的研究。结果表明:进气压力及柴油喷射时刻会影响缸内浓度分层进而影响燃烧过程,而汽油喷射时刻影响不明显;在汽油采用进气道结合缸内直喷的混合喷射策略下,增加缸内直喷汽油量可以进一步增强缸内的混合气浓度分层,延长燃烧持续期,降低缸内的最高燃烧压力和压力升高率,实现更低的燃烧温度。仿真计算结果显示:若保证碳烟和NOx排放在限值内且油耗有所降低,可将平均有效指示压力(IMEP)拓展至1.6MPa;将IMEP拓展到1.7MPa后,增加汽油的预混比例并不能提高IMEP,但对排放略有改善,相应的压力升高率和燃烧压力提高。     

船用直喷式天然气发动机喷射策略的优化

利用CONVERGE软件基于L23/30DF型船用天然气发动机建立了双天然气喷嘴、双引燃柴油喷嘴的直喷天然气发动机的缸内燃烧过程的CFD计算模型,计算了不同的柴油和天然气喷射时刻和间隔下发动机缸内燃烧和排放过程.结果 表明:引燃柴油的喷射时刻及其与天然气喷射时刻的间隔,对直喷式天然气发动机燃烧和排放性能有重要影响.当喷...     

燃用直喷汽油-预混醇混合气的汽油机燃烧特性

通过进气道喷射乙醇/正丁醇方式形成预混醇混合气,通过缸内直喷汽油方式形成分层汽油混合气,研究了相同循环供油总能量下汽油机的燃烧与排放特性.结果表明,在进气过程直喷汽油时,汽油机的平均指示有效压力和指示热效率均高于在压缩过程中直喷汽油时的值,并且前者的碳氢化合物和一氧化碳排放更低.在进气过程中直喷汽油时,进气道喷醇-直喷汽油方式与仅采用进气道喷醇方式下汽油机的指示热效率相近.进气道喷乙醇-直喷汽油(E-GDI)和进气道喷正丁醇-直喷汽油(B-GDI)混合气形成方式下汽油机的效率与排放优于仅采用汽油直喷(GDI)形成混合气方式下的值,而且E-GDI方式下汽油机的指示热效率最高.直喷汽油压力对汽油机燃烧的影响与汽油直喷时刻有关.汽油直喷时刻越早,它对汽油机平均指示有效压力的影响越小.     

直喷汽油对HPCC大负荷工况影响的数值模拟

利用三维计算流体动力学(CFD)软件CONVERGE,通过数值模拟的方法,对燃油预混比例、汽油喷射时刻、柴油喷射时刻和柴油喷射量4个参数进行优化,系统研究了缸内直喷汽油对高比例预混燃烧(HPCC)大负荷工况的影响.结果表明:汽油采用进气道结合缸内直喷的混合喷射策略可以增强缸内的混合气浓度分层;采用该喷油策略计算得到的平均指示有效压力(IMEP)和压力升高率分别为1.350,MPa、0.520,MPa/(°)CA,相比于基准工况的1.346,MPa和0.893,MPa/(°)CA,在保证IMEP不变的前提下,压力升高率和NOx排放分别降低了41%,和46%,,soot排放略有升高.采用汽油混合喷射结合柴油缸内直喷是控制压力升高率和拓展HPCC运行负荷上限的有效措施之一.     

喷油时刻对汽油/乙醇发动机性能的影响

通过一台Yamaha YBR250发动机原机,进行乙醇直喷(EDI)与汽油进气道喷射(GPI)的改装,研究了EDI喷油时刻对发动机缸内混合气形成、燃烧和排放的影响,同时建立了EDI结合GPI发动机的三维计算模型,对试验工况进行了数值模拟.分别对喷雾模型和燃烧模型进行了试验标定,结果表明:通过改变EDI喷油时刻,进气涡流与喷雾带动气流的运动共同作用于缸内燃料的蒸发雾化,可以在火花塞附近形成不同程度的燃料浓区;延迟EDI喷油时刻至100°CA BTDC,能够有效地协同壁面传热以及乙醇蒸发作用,降低点火时刻缸内温度,从而降低最大爆发压力和缸内燃烧温度;相对于早喷工况,EDI喷油时刻为100°CA BTDC的工况能够有效降低缸内HC及NO排放.     

柴油/汽油反应活性控制压燃发动机喷油协调控制与排放特性研究

对某4缸高压共轨柴油机进气道进行改造,搭建了柴油/汽油双燃料反应活性控制压燃(reactivity controlled compression ignition,RCCI)发动机专用试验台架,设计了柴油/汽油双燃料RCCI燃烧汽油喷射控制策略,实现了全工况下汽油与柴油的协调喷射控制,系统地研究了不同运行工况下,不同汽油替代率对柴油机燃烧与排放性能的影响规律。结果表明:采用柴油/汽油双燃料RCCI燃烧控制策略,发动机可在其运行工况范围内实现高效清洁燃烧,随着汽油替代率的增加,发动机缸内最高压力逐渐增大,缸压峰值出现时刻推迟,放热率峰值降低,燃烧持续期延长,燃油消耗率降低,有效热效率升高,全碳氢、CO排放增加,NOx和碳烟排放降低。     

喷油定时对柴油机超多喷孔预混合燃烧影响研究

柴油机低温预混合燃烧能够同时大幅度降低NOx和碳烟(soot)排放,本研究采用大量废气再循环(EGR)实现低温燃烧来降低NOx排放,采用超多喷孔喷油嘴并结合高压喷射来缩短喷油持续期,实现预混合燃烧从而降低soot排放,主要对喷油定时如何影响柴油机超多喷孔预混合燃烧性能进行了试验研究,选定4个试验工况,通过改变喷油定时来测试柴油机性能,结果显示随着喷油始点从上止点前向后推迟,各工况的NOx和soot排放都有不同程度的同时下降,有别于传统燃烧方式,但HC,CO,比油耗(BSFC)有所升高。     

不同喷射时刻下缸内直喷天然气发动机的燃烧特性

开展了天然气高压缸内直喷发动机不同喷射时刻时的燃烧特性研究。研究结果表明：燃料喷射时刻对发动机性能及排放有较大影响,喷射太迟会导致天然气和空气混合时间短,混合效果差,燃烧持续期长,放热速率慢。喷射过早会导致充量系数下降,燃料容易进入燃烧室狭缝间隙处,造成较高的HC排放。对于给定转速,发动机存在一个最佳燃料喷射提前角,此时缸内最高压力值最大,最大压力升高率和最大放热率最大,放热速率快,燃烧过程等容度好,火焰发展期、快速燃烧期和燃烧持续期短,发动机热效率高,HC、CO排放也维持较低水平。     

火花点火天然气发动机起动阶段HC排放特性研究

为降低天然气发动机起动阶段的HC排放,在一台6缸火花点火天然气发动机上进行了起动试验研究。控制起动阶段的喷射脉宽和点火提前角,采集起动后1min内的转速和排放数据。试验结果表明:在一定范围内,HC排放随喷射脉宽和点火提前角的增加而增加。为保证顺利起动并有较低的HC排放,起动初始阶段应采用较大的喷射脉宽和较大的点火提前角,而转速稳定后采用逐渐减小的喷射脉宽和点火提前角。     

Effects of fuel combination and IVO timing on combustion and emissions of a dual-fuel HCCI combustion engine

This paper experimentally and numerically studied the effects of fuel combination and intake valve opening (IVO) timing on combustion and emissions of an n-heptane and gasoline dual-fuel homogeneous charge compression ignition (HCCI) engine. By changing the gasoline fraction (GF) from 0.1 to 0.5 and the IVO timing from –15°CA ATDC to 35°CA ATDC, the in-cylinder pressure traces, heat release behaviors, and HC and CO emissions were investigated. The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing, lengthen the combustion duration, and decrease the peak heat release rate and the maximum average combustion temperature, whereas the IVO timing has a more obvious influence on combustion than GF. HC and CO emissions are decreased with reduced GF, advanced IVO timing and increased operational load.     

掺混比例和喷射定时对二甲醚-乙醇发动机燃烧和排放的影响

在一台电控共轨发动机上,试验研究了乙醇掺混比例和喷射定时对二甲醚-乙醇混合燃料燃烧及排放的影响。结果表明:随乙醇比例的增加,滞燃期延长,燃烧持续期缩短,最大压力升高率上升。随喷射推迟,滞燃期延长,燃烧相位延后,燃烧持续期在纯二甲醚时延长,而在掺混乙醇时则先延长后缩短,最大压力升高率先下降后上升。掺混乙醇和推迟喷射使预混燃烧比例增加。随喷射推迟,混合燃料的排气温度升高,喷射推迟到上止点后,排气温度随乙醇比例的增加而升高,排气温度高,则废气能量高,增压器增压比大,进气流量大,导致缸内压缩压力升高。在上止点前喷射时,掺混乙醇能使HC和CO排放保持在较低范围的同时,一定程度降低NO_x排放,掺混15%的乙醇较纯二甲醚最大降低约11%NO_x排放。随推迟喷射,NO_x排放降低,最大降幅达52%,在过分推迟燃料喷射时,因热效率低,循环喷射量增加,含15%乙醇混合燃料的NO_x排放会高于纯二甲醚。HC和CO排放随喷射推迟而升高,且升高幅度增大。     

增压直喷汽油机燃油喷射特性对排放影响的试验研究

基于某1.5L涡轮增压直喷汽油机,搭建试验测试系统,采用试验匹配测试方法研究了喷油模式、喷油时刻、喷油比例、喷油压力等决定燃油喷射特性的关键参数对碳烟排放的影响。试验结果表明:单次喷油模式下在部分负荷时,喷油越提前,碳烟排放越多;在全负荷时,喷油越推迟,碳烟排放越多。在多次喷油模式下,随第一次喷油的推迟碳烟排放降低,随第二、三次喷油的推迟碳烟排放增加。提高喷油压力对部分负荷工况燃烧及排放改善不明显,但外特性工况碳烟排放显著下降,碳氢化合物排放总量也大幅度降低,缸内燃烧速度加快,燃烧稳定性提高,有效燃油消耗率降低约2%。     

Study on combustion and emission characteristics of a n-butanol engine with hydrogen direct injection under lean burn conditions

The n-butanol fuel, as a renewable and clean biofuel, could ease the energy crisis and decrease the harmful emissions. As another clean and renewable energy, hydrogen properly offset the high HC emissions and the insufficient of dynamic property of pure n-butanol fuel in SI engines, because of the high diffusion coefficient, high adiabatic flame velocity and low heat value. Hydrogen direct injection not only avoids backfire and lower intake efficiency but also promotes to form in-cylinder stratified mixture, which is helpful to enhance combustion and reduce emissions. This experimental study focused on the combustion and emissions characteristics of a hydrogen direct injection stratified n-butanol engine. Three different hydrogen addition fractions (0%, 2.5%, 5%) were used under five different spark timing (10° ,15° ,20° ,25° ,30° CA BTDC). Engine speed and excess air ratio stabled at 1500 rpm and 1.2 respectively. The direct injection timing of the hydrogen was optimized to form a beter stratified mixture. The obtained results demonstrated that brake power and brake thermal efficiency are increased by addition hydrogen directly injected. The BSFC is decreased with the addition of hydrogen. The peak cylinder pressure and the instantaneous heat release rate raises with the increase of the hydrogen addition fraction. In addition, the HC and CO emissions drop while the NOx emissions sharply rise with the addition of hydrogen. As a whole, with hydrogen direct injection, the power and fuel economy performance of n-butanol engine are markedly improved, harmful emissions are partly decreased.     

Numerical study on effects of hydrogen direct injection on hydrogen mixture distribution,combustion and emissions of a gasoline/hydrogen SI engine under lean burn condition

A numerical study on effects of hydrogen direct injection on hydrogen mixture distribution, combustion and emissions was presented for a gasoline/hydrogen SI engine. Under lean burn conditions, five different direct hydrogen injection timings were applied at low speeds and low loads on SI engines with direct hydrogen injection (HDI) and gasoline port injection. The results were showed as following: firstly, with the increase of hydrogen direct injection timing, the hydrogen concentration near the sparking plug first increases and then decreases, reaching the highest when hydrogen direct injection timing is 120°CA BTDC: Secondly, hydrogen can speed up the combustion rate. The main factor affecting the combustion rate and efficiency is the hydrogen concentration near the sparking plug: Thirdly, in comparing with gasoline, the NO_X emissions with hydrogen addition increase by an average of 115%. For different hydrogen direct injection timings, the NO_X emissions of 120°CA BTDC is the highest, which is 29.9% higher than the 75°CA BTDC. The hydrogen addition make the NO_X emissions increase in two ways. On the one hand, the average temperature with hydrogen addition is higher. On the other hand, the temperature with hydrogen addition is not homogeneous, which makes the peak of temperature much higher. In a word, the main factor of NO_X emissions is the size of high temperature zone in the cylinder: Finally, because the combustion is more complete, in comparing with gasoline, hydrogen addition can reduce the CO and HC emissions by 32.2% and 80.4% respectively. Since a more homogeneous hydrogen mixture distribution can influence a lager zone in the cylinder and reduce the wall quenching distance, these emissions decrease with the increase of hydrogen direct injection timing. The CO and HC emissions of 135°CA BTDC decrease by 41.5% and 71.4%, respectively, compared to 75°CA BTDC.     

Effects of Fischer-Tropsch diesel fuel on combustion and emissions of direct injection diesel engine

Effects of Fischer-Tropsch (F-T) diesel fuel on the combustion and emission characteristics of a single-cylinder direct injection diesel engine under different fuel delivery advance angles were investigated. The experimental results show that F-T diesel fuel exhibits shorter ignition delay, lower peak values of premixed burning rate, lower combustion pressure and pressure rise rate, and higher peak value of diffusion burning rate than conventional diesel fuel when the engine remains unmodified. In addition, the unmodified engine with F-T diesel fuel has lower brake specific fuel consumption and higher effective thermal efficiency, and presents lower HC, CO, NO_x and smoke emissions than conventional diesel fuel. When fuel delivery advance angle is retarded by 3 crank angle degrees, the combustion duration is obviously shortened; the peak values of premixed burning rate, the combustion pressure and pressure rise rate are further reduced; and the peak value of diffusion burning rate is further increased for F-T diesel fuel operation. Moreover, the retardation of fuel delivery advance angle results in a further significant reduction in NO_x emissions with no penalty on specific fuel consumption and with much less penalty on HC, CO and smoke emissions.