Examination of nanoparticles from gasoline direct-injection (GDI) engines using transmission electron microscopy (TEM)

Gasoline direct-injection (GDI) engines have been reported to produce significantly more particulate matter (PM) mass and particulate number (PN) emissions than do port-fuel-injection (PFI) spark ignition engines. Because smallsized particles are of great concern in terms of their regulation, transmission electron microscopy (TEM) was used to evaluate the sizes of primary and aggregate particles that were thermophoretically collected from three different GDI engines under various engine operating conditions. A low load and retarded fuel injection generally reduced the particle size. Consequently, when the fuel injection timing was delayed at low loads, primary and aggregate particles became extremely small. In particular, a number of nanoparticles were sub-23-nm particles. Careful high-resolution TEM (HRTEM) analyses provided the first evidence that these nanoparticles are solid carbon particles with clear fringe patterns and young soot (and/or highly condensed semi-volatiles) with amorphous carbon patterns. Therefore, this result suggests that the current cut-off size at 23 nm for PN regulation in Euro 6 must be further reduced to include sub-23-nm carbon nanoparticles.     

理论空燃比下废气再循环率对汽油机性能的影响

为了提高某增压汽油机的性能,将其压缩比提高到11.5,并加装一套EGR循环系统。通过台架试验,在低速小负荷和中速中负荷工况下,研究了理论空燃比下废气再循环率对改造后汽油机性能的影响。结果表明:当EGR率小于20%时,采用合适的EGR率配合优化的点火时刻,可以使该发动机燃烧稳定,在保证发动机动力性的同时,指示热效率随着EGR率的增加不断升高;与无EGR时相比,EGR率为20%时,有效燃油消耗率在低速小负荷工况下降低了约4.5%,中速中负荷工况下降低了9.7%;随着EGR率的增加,THC排放增加,而NOx排放显著降低,CO排放在低速小负荷时出现上下波动的现象,而在中速中负荷工况时,随着EGR率的增加不断降低。     

Experimental investigation and comparison of nanoparticle emission characteristics in light-duty vehicles for two different fuels

In recent years, particle number emissions rather than particulate mass emissions in automotive engines have become the subject with controversial discussions. Recent results from studies of health effects imply that it is possible that particulate mass does not properly correlate with the variety of health effects attributed to engine exhaust. The concern is now focusing on nano-sized particles emitted from I. C. engines. In this study, particulate mass and particle number concentration emitted from light-duty vehicles were investigated for a better understanding of the characteristics of the engine PM from different types of fuels, such as gasoline and diesel fuel. Engine nano-particle mass and size distributions of four test vehicles were measured by a condensation particle counter system, which is recommended by the particle measurement program in Europe (PMP), at the end of a dilution tunnel along a NEDC test mode on a chassis dynamometer. We found that particle number concentrations of diesel passenger vehicles with DPF system are lower than gasoline passenger vehicles, but PM mass has some similar values. However, in diesel vehicles with DPF system, PM mass and particle number concentrations were greatly influenced by PM regeneration. Particle emissions in light-duty vehicles emitted about 90% at the ECE15 cycle in NEDC test mode, regardless of vehicle fuel type. Particle emissions at the early cold condition of engine were highly emitted in the test mode.     

PFI汽油机排气微粒数浓度及粒径分布研究

在不同转速和负荷下,用快速微粒光谱仪(DMS500)对PFI汽油机排气微粒的数浓度和粒径分布进行了测量.结果表明:在中低负荷下,PFI汽油机产生的微粒几乎全部为纳米级核模态粒子,随着负荷的增加,微粒数浓度单调增加,并且峰值粒径向粒径增大方向迁移;微粒的几何平均直径(GMD)和中位直径(CMD)都是随着负荷的增加而逐渐增...     

轻型CNG车颗粒物排放特性研究

对同一台轻型两用燃料（C N G和汽油）车使用同一批次基准天然气和基准汽油,在底盘测功机上进行NEDC ,FTP75和WLTC循环对比试验,使用CVS定容取样系统和ELPI设备分析颗粒物等排放。研究发现：3种循环中,试验车辆燃用CNG和汽油,排放颗粒物在 Dp ＝40 nm和 Dp ＝330 nm附近均出现峰值,Dp ＝40 nm处汽油峰值远高于CNG ,Dp ＝330 nm处CNG峰值略高于汽油;CNG的PN和PM的排放率随车速的升高而增大,在较低的匀速工况下增长幅度较小,高速工况下增长幅度较大;CNG在NEDC循环中排放的核态和聚集态颗粒物各占50％左右,FTP75和WLTC循环中排放的聚集态颗粒物占比高于NEDC ;CNG在NEDC循环中单位里程颗粒数和颗粒总数最多,FTP75和WLTC循环中单位里程颗粒数基本相同;WLTC循环中排放的颗粒物质量总量最多,FTP75和NEDC循环中排放的颗粒物质量总量基本相同;FTP75和WLTC循环中单位里程排放的颗粒物质量基本相同,约为N EDC循环的2倍。     

混合气分层对HCCI汽油机极限负荷和燃烧特性的影响

对比研究HCCI汽油机在不同空燃比下采用混合气分层策略时的极限负荷、NOx排放量和燃油经济性,考察了在此策略下过量空气系数λ和EGR率对HCCI发动机燃烧特性的影响。结果表明,混合气分层压缩燃烧模式能有效降低HCCI燃烧的压力升高率,具有拓展负荷范围的潜力,但同时也使NOx排放增加;适当的过量空气系数能在一定程度上改善HCCI发动机的燃烧特性,采用9%的EGR率时发动机油耗率最低,具有明显节油效果。     

Effect of fuel choice on nanoparticle emission factors in LPG-gasoline bi-fuel vehicles

Nanoparticle and gas-phase emission factors are presented for a liquefied petroleum gas (LPG) passenger vehicle and are compared to gasoline operation. A bi-fuel LPG-gasoline vehicle certified for use on either fuel was used as the test vehicle so that a direct comparison of the emissions could be made based on fuel choice. These values were considered along with previous studies to determine the relative change in particulate emissions due to fuel choice over a wide range of vehicles and operating conditions. The vehicle examined in this study was tested on a chassis dynamometer for both steadystate and transient conditions. Transient test cycles included the US FTP72 driving cycle, Japanese driving cycle and modified Indian driving cycle while steady-state tests were done at vehicle speeds ranging from 10–90 km/hr in various transmission gears. Exhaust particle size distributions were measured in real-time using a differential mobility spectrometer (DMS50), and particle number and particle mass emission factors were calculated. For both fuels, the majority of the particles ranged from 5 to 160 nm in terms of particle diameter, with typically more than 85% of the particles in the nucleation mode (between 5–50 nm). In most cases, the vehicle produced a greater fraction of larger (accumulation mode) particles when fuelled on LPG. Using the data in the literature as well as the data in the current study, gasoline fuel produces 4.6 times more particles in terms of number and 2.1 times more particles in terms of mass.     

负荷控制方式对甲醇发动机性能影响的试验研究

在1台2L柴油机改装的点火式甲醇发动机上分别采用节气门、节气门联合EGR以及单纯EGR的方式来控制发动机负荷,试验负荷选择了全负荷的50%和75%,过量空气系数保持在1附近,调整点火角,进行动力性和排放性试验。研究发现:两种负荷下都是采用节气门联合EGR控制负荷时发动机的动力性和经济性最好;两种负荷下的HC排放随控制方式的不同而不同,但均为节气门控制负荷时HC排放最低;两种负荷下的CO排放随控制方式的不同而不同,但都是节气门控制负荷时CO排放最高;两种负荷下的NOx排放规律相似,均为节气门开度越大,NOx排放越低。     

Operating strategy for gasoline/diesel dual-fuel premixed compression ignition in a light-duty diesel engine

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.     

EGR对轻型柴油机超细颗粒排放的影响

基于1台匹配废气再循环(EGR)系统的轻型柴油机,在中低负荷下研究了EGR对发动机超细颗粒排放的影响.研究发现:各工况下,随EGR率的增大,颗粒排放中核模态颗粒数量浓度在各粒径下有所减少,核模态颗粒排放数量速率和质量速率有减少趋势,且在最大扭矩转速的低负荷工况更加明显;积聚态颗粒数量浓度在各粒径下都增加,积聚态颗粒排放数量和质量速率也都增加,且中负荷时更加明显,而积聚态颗粒数量浓度峰值粒径基本没有改变.随EGR率的增大,总的超细颗粒排放数量速率在最大扭矩转速的低负荷工况减小,而其他工况都明显增加.由于积聚态颗粒总质量浓度占超细颗粒总质量浓度比例达99%,所以超细颗粒排放质量速率也都增加,几何平均粒径也都明显增大.在低负荷较低EGR率和中负荷较大EGR率时,过高的喷油压力都将使超细颗粒排放数量速率增加.     

纯柴油、柴油/CNG两种燃烧模式下应用EGR的发动机性能研究

在一台单缸柴油机上加装天然气电控喷射系统，改造成柴油／CNG双燃料发动机。通过示功图、放热率、排放特性和经济性的实验与分析，研究了纯柴油和双燃料两种燃烧模式下应用冷却EGR的效果。研究表明：不管是纯柴油模式还是双燃料模式，使用EGR之后，NOx都有大幅度降低；纯柴油模式使用EGR之后，会带来碳烟排放的恶化，但是对于双燃料模式，当EGR比例在22％以内，负荷小于75％时，不会造成碳烟排放的恶化。随着EGR比例的增大，燃烧放热率曲线由双峰过渡到单峰形状，具有均质压燃(HCCI)燃烧过程的特征。     

在EQ6100型汽油机上获取最佳EGR率的试验研究

试验结果表明，在各种负荷工况下，ＥＱ６１００型汽油机采用ＥＧＲ后其ＮＯｘ排放都显下降，但ＨＣ、ＣＯ排放及燃油消耗率随ＥＧＲ率的变化则较为复杂，而因各工况下均存在一个最佳ＥＧＲ率。通过试验，给出了ＥＱ６１００型汽油机２０００ｒ／ｍｉｎ下最佳ＥＧＲ率随负荷变化的曲线，为其排气背压控制ＥＧＲ系统的设计提供了依据。     

Effects of gasoline, diesel, LPG, and low-carbon fuels and various certification modes on nanoparticle emission characteristics in light-duty vehicles

This study was focused on experimental comparisons of the effects of various vehicle certification modes on particle emission characteristics of light-duty vehicles with gasoline, diesel, LPG, and low-carbon fuels such as bio-diesel, bioethanol, and compressed natural gas, respectively. The particulate matter from various fueled vehicles was analyzed with the golden particle measurement system recommended by the particle measurement programme, which consists of CVS, a particle number counter, and particle number diluters. To verify particle number and size distribution characteristics, various vehicle emission certification modes such as NEDC, FTP-75, and HWFET were compared to evaluate particle formation with both CPC and DMS500. The formation of particles was highly dependent on vehicle speed and load conditions for each mode. In particular, the particle numbers of conventional fuels and low-carbon fuels sharply increased during cold start, fast transient acceleration, and high-load operation phases of the vehicle emission tests. A diesel vehicle fitted with a particulate filter showed substantial reduction of particulate matter with a number concentration equivalent to gasoline and LPG fuel. Moreover, bio-fuels and natural gas have the potential to reduce the particulate emissions with the help of clean combustion and low-carbon fuel quality compared to non-DPF diesel-fueled vehicles.     

铁基燃油添加剂对柴油机颗粒排放影响的试验研究

基于发动机试验台架,对柴油中添加微量的铁基燃油添加剂进行了试验,从颗粒物数量浓度和粒径的分布特性、排气烟度、颗粒物的氧化特性等方面研究了燃油添加剂对柴油机颗粒物排放的影响。研究结果表明：燃油添加剂能降低柴油机排气温度和排气烟度。加入添加剂后,核模态颗粒数量浓度增加,峰值粒径也增加;积聚态颗粒数量浓度无明显变化;颗粒物总数量浓度增加,但添加剂浓度对颗粒数量浓度影响较小。添加剂使颗粒物中SOF含量增加,同时也使得微粒的氧化表观活化能和起燃温度都降低。     

Exhaust emissions and its control methods in compression ignition engines: A review

Extensive usage of automobiles has certain disadvantages and one of them is its negative effect on environment. Carbon dioxide (CO₂), carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and particulate matter (PM) come out as harmful products during incomplete combustion from internal combustion (IC) engines. As these substances affect human health, regulatory bodies impose increasingly stringent restrictions on the level of emissions coming out from IC engines. This trend suggests the urgent need for the investigation of all aspects relevant to emissions. It is required to modify existing engine technologies and to develop a better after-treatment system to achieve the upcoming emission norms. Diesel engines are generally preferred over gasoline engines due to their undisputed benefit of fuel economy and higher torque output. However, diesel engines produce higher emissions, particularly NO_x and PM. Aftertreatment systems are costly and occupy more space, hence, in-cylinder solutions are preferred in reducing emissions. Exhaust gas recirculation (EGR) technology has been utilized previously to reduce NO_x. Though it is quite successful for small engines, problem persists with large bore engines and with high rate of EGR. EGR helps in reducing NO_x, but increases particulate emissions and fuel consumption. Many in-cylinder solutions such as lower compression ratios, modified injection characteristics, improved air intake system etc. are required along with EGR to accomplish the future emission norms. Modern combustion techniques such as low temperature combustion (LTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) etc. would be helpful for reducing the exhaust emissions and improving the engine performance. However, controlling of autoignition timing and achieving wider operating range are the major challenges with these techniques. A comprehensive review of diesel engine performance and emission characteristics is given in this paper.     

Particulate Matter and Particle-Bound PAHs Emissions from Gasoline Direct Injection (GDI) Engine with Methanol-Gasoline Blended Fuel During Start

The effects of coolant’s temperature on emissions of particulate matters (PM) and particle-bound polycyclic aromatic hydrocarbons (PAHs) from a gasoline direct injection (GDI) engine were studied during the start process using gasoline (M0) and gasoline mixed with methanol in 15 % volume (M15). The engine worked at a certain idle speed automatically under different coolant’s temperature conditions after successful start. The experimental data was recorded from 0 to 40 seconds during the start. Results indicated that, there are significant differences in PM and particle-bound PAHs emissions between cold and warm start conditions. Particulate size distribution was measured with the Engine Exhaust Particle Sizer (EEPS) 3090. Compared with M0 fuel, the PM emission of M15 fuel decreased significantly, especially nucleation-mode particulate emission. The mass emission of PM was measured using the Gravimetric method. A same variation trend in PM mass emissions can be inferred for both fuels, i.e. it decreases while the coolant’s temperature increases. Compared with M0 fuel, the PM mass with M15 fuel reduces by 80 % at 20 oC coolant’s temperature. Agilent 7000B GC-QQQ was used to provide both qualitative and quantitative analysis on PAHs. The application of M15 fuel reduces the concentrations of most PAH species compared with M0 fuel, except those with smaller aromatic rings. In addition, Benzo(a)pyrene equivalent toxicity (BEQ) is calculated to evaluate the toxicity of PAHs emissions. The toxicity decreases when the GDI engine starts with higher coolant’s temperature or with M15 fuel.     

测量条件对柴油机排放PM尺寸分布的影响

研究了不同测量条件对柴油机PM尺寸与浓度分布测量的影响,在一台单缸柴油机上用SMPS测量装置测量了不同运转条件下柴油机PM排放,试验中采用不同的稀释比、稀释空气温度、取样点位置等,在大量的试验研究基础上,分析了柴油机PM排放的特征和主要影响因素。结果表明,随稀释比增加,PM尺寸趋向于累积模式分布或粗粒子模式分布,其浓度趋于降低;随着稀释空气温度的升高,PM质量和数量也相应降低,低负荷时PM峰值浓度移向细小颗粒的碳核模式区域;取样点位置远离排气出口,PM浓度逐渐减小,累积模式尺寸的PM数增多。     

稀燃条件下甲醇汽油混合燃料颗粒物排放特性

在1台GDI增压汽油机上,进行了稀燃发动机燃用M0,M10和M20(其中M0为汽油,M10为甲醇体积分数10%、汽油体积分数90%的混合燃料,以此类推)甲醇汽油混合燃料的试验,研究了在稀燃条件下甲醇汽油混合燃料对GDI发动机颗粒粒径分布特性、数量浓度特性和质量浓度特性的影响。试验结果表明:在稀燃条件下,随着甲醇比例的增加颗粒数量浓度峰值逐渐增大,颗粒数量浓度随粒径分布呈现出双峰分布;颗粒中的核态颗粒和积聚态颗粒的总数量都随甲醇比例的增加而增加,其中M20的积聚态和核态颗粒数量浓度最大;颗粒粒径峰值都随着甲醇比例的增加逐渐增大,并且核态颗粒粒径峰值主要集中在20.54~31.62nm,积聚态颗粒粒径峰值主要集中在56.23~100nm;颗粒质量浓度随甲醇比例的增加而增大,粒径分布在316~700nm的积聚态颗粒明显增多,积聚态颗粒质量浓度随粒径分布的范围明显增加,质量浓度也相应增加,而粒径分布在56.23~316nm范围内的颗粒质量浓度却在降低。     

乙醇汽油对车辆颗粒物排放的影响

在符合国Ⅰ、国Ⅲ、国Ⅴ标准的3辆试验车上,分别燃用国Ⅴ汽油、低芳烃E10、低烯烃E10 3种燃料,进行了NEDC和WLTC工况下的常温冷起动排放试验,重点对颗粒物(PM)排放量和粒子数量(PN)进行分析。结果表明:在两种工况下,燃用乙醇汽油相比普通汽油能大幅降低车辆的PM排放,低芳烃E10对国Ⅰ和国Ⅲ车辆PM降低效果最明显,分别下降19%和35%,低烯烃E10对国Ⅴ车辆PM降低效果最好,下降46%;在WLTC工况下燃用乙醇汽油能大幅降低车辆PN排放,其中低芳烃E10平均降低43%,低烯烃E10平均降低32%。     

纳米燃油添加剂对柴油机颗粒物排放特性的影响

在186FA柴油机上对质量分数为50mg/kg和100mg/kg的CeO2或Co3O4纳米颗粒-柴油混合燃料进行颗粒物排放特性台架试验,采用扫描电镜和热重分析仪对采集到的颗粒物样品进行微观结构形貌及热重特性分析。结果表明:纳米CeO2和Co3O4颗粒均可改善柴油机颗粒物排放,与0号柴油相比,混合燃料颗粒物比排放量下降16.4%~35.9%;混合燃料颗粒物排放的粒径分布仍呈单峰分布的特点,峰值均在0.56~1.0μm区间内,微观形态下的粒径和孔隙率明显变小,团聚程度提高;混合燃料燃烧过程中颗粒物发生氧化反应的起燃温度、失重率峰值温度及燃尽温度均有所降低,最大失重率明显增加。