Effects of lubricant-fuel mixing on particle emissions in a single cylinder direct injection spark ignition engine

Gasoline direct injection (GDI) engines emit less carbon dioxide (CO2) than port fuel injection (PFI) engines when fossil fuel conditions are the same. However, GDI engines emit more ultrafine particulate matter, which can have negative health effects, leading to particulate emission regulations. To satisfy these regulations, various studies have been done to reduce particulate matter, and several studies focused on lubricants. This study focuses on the influence of lubricant on the formation of particulate matter and its effect on particulate emissions in GDI engines. An instrumented, combustion and optical singe-cylinder GDI engine fueled by four different lubricant-gasoline blends was used with various injection conditions. Combustion experiments were used to determine combustion characteristics, and gaseous emissions indicated that the lubricant did not influence mixture homogeneity but had an impact on unburned fuels. Optical experiments showed that the lubricant did not influence spray but did influence wall film formation during the injection period, which is a major factor affecting particulate matter generation. Particulate emissions indicated that lubricant included in the wall film significantly affected PN emissions depending on injection conditions. Additionally, the wall film influenced by the lubricant affected the overall particle size and its distribution.

Effect of LP-EGR on the Emission Characteristics of GDI Engine

Exhaust gas recirculation (EGR) can improve the fuel economy of gasoline direct-injection (GDI) engines, but at the same time it will have a significant impact on emissions. In this paper, the effects of low-pressure exhaust gas recirculation (LP-EGR) and its rate on the main gaseous and particulate emission characteristic of a GDI engine were investigated. The results showed that the particle size distribution of the GDI engine presented bimodal peaks in nucleation and accumulation mode, and the nucleation mode particles comprised the vast majority of the total particles. The effect of LP-EGR on emissions depended on the engine conditions. At low and medium speed, the particle emissions increased with the increase in the EGR rate, while at high speed, a reduction in the particle emission was observed. When the engine operated in full load condition, an increase in the EGR rate reduced the particle number (PN) concentration significantly, but increased the particle mass (PM) concentration. In terms of the gaseous emission, the EGR could reduce as much as 80% of the NOx emission; however, the total hydrocarbons (THC) emission presented an increased trend, and the maximum increase reached 23.5%. At low and medium loads, the EGR could reduce the CO emission, but at high load, the CO emission worsened with the EGR.

Impact of Blow-By Gas and Endgap Ring Position on the Variations of Particle Emissions in Gasoline Engines

Particulate emission from internal combustion engines is a complex phenomenon that needs to be understood in order to identify its main factors. To this end, it appears necessary to study the impact of unburned gases, called blow-by gases, which are reinjected into the engine intake system. A series of transient tests demonstrate their significant contribution since the particle emissions of spark-ignition engines are 1.5 times higher than those of an engine without blow-by with a standard deviation 1.5 times greater. After analysis, it is found that the decanter is not effective enough to remove completely the oil from the gases. Tests without blow-by gases also have the advantage of having a lower disparity, and therefore of being more repeatable. It appears that the position of the “endgap” formed by the first two rings has a significant impact on the amount of oil transported towards the combustion chamber by the backflow, and consequently on the variation of particle emissions. For this engine and for this transient, 57% of the particulate emissions are related to the equivalence ratio, while 31% are directly related to the ability of the decanter to remove the oil of the blowby gases and 12% of the emissions come from the backflow. The novelty of this work is to relate the particles fluctuation to the position of the endgap ring.

Effects of diesel from direct and indirect coal liquefaction on combustion and emissions in a six-cylinder turbocharged diesel engine

The aim of this study is to evaluate the effects of diesel from direct coal liquefaction (DDCL) and diesel from indirect coal liquefaction (DICL) on combustion and emissions. A six-cylinder turbocharged diesel engine fueled with DDCL, DICL, petroleum diesel (PD), 58% DDCL, and 42% DICL blended by volume (BD58) is used. The experiments are carried out at 1400 and 2300rpm engine speeds and various engine loads (10%, 25%, 50%, 75%, and 90% of the full-load). The results show that the brake thermal efficiency (BTE) of PD was higher than that of CTL (the maximum difference was 2%) at medium and high loads. At 10% load of 1400 rpm, the CO, HC and formaldehyde emissions of DDCL are 88.9%, 44.3% and 26.5% higher than those of PD respectively, and the CO, HC, and formaldehyde emissions of DICL are 30.1%, 15.3%, and 15.2% lower than those of PD. The differences among four fuels decrease rapidly with the increase of load. The NOX emissions of PD are the highest due to high nitrogen content (102.3 μg/g) and low hydrogen-carbon (H/C) ratio. The fuel with higher cetane number has less formaldehyde emission at low loads, while the fuel with lower H/C has less formaldehyde emission at high loads. The particle size distribution shows a bimodal shape at different loads and the peak particle size of accumulation mode and nucleation mode all increases with the increase of load. The particulate emission of different fuels from high to low is the order of PD > DDCL > BD58 > DICL. In addition, the emissions of polycyclic aromatic hydrocarbons (PAHs) and toxicity equivalent (TE) of PD are highest at all loads. The proportion of soluble organic fractions (SOF) from DDCL, DICL, and BD58 is higher than that of PD.

Effect of injection and ignition timing on a hydrogen-lean stratified charge combustion engine

Hydrogen can be used as a fuel for internal combustion engines to realize a carbon-neutral transport society. By extending the lean limit of spark ignition engines, their efficiency, and emission characteristics can be improved. In this study, stratified charge combustion (SCC) using monofueled hydrogen direct injection was used to extend the lean limit of a spark ignition engine. The injection and ignition timing were varied to examine their effect on the SCC characteristics. An engine experiment was performed in a spray-guided single-cylinder research engine, and the nitrogen oxide and particulate emissions were measured. Depending on the injection timing, two different types of combustion were characterized: mild and hard combustion. The advancement and retardation of the ignition timing resulted in a high and low combustion stability, respectively. The lubricant-based particulate emission was attributed to the in-cylinder temperature and area of the flame surface. Therefore, the results of the study suggest that the optimization of the hydrogen SCC based on the injection and ignition timing could contribute to a clean and efficient transport sector.