Effect of Biofuels on Nanoparticle Emissions from Spark- and Compression-ignited Single-cylinder Engines with Same Exhaust Displacement Volume

Abstract

Nanosized particles emitted from automotive engines continue to attract concern because of their adverse health effects and their impact on the environment. Automotive engines are a major source of fine and ultrafine particles emitted into the atmosphere. Through stricter emission regulations and the introduction of advanced technologies, the specific particulate mass emissions (in g/km and g/kWh) from internal combustion engines have decreased by about 1 order of magnitude since the 1980s. However, the number concentration of nanoparticles (No./m 3 ) emitted from internal combustion engines may continue to increase considerably and has recently attracted the attention of the Particle Measurement Programme (PMP). This program is intended to evaluate engine nanoparticle measurement systems for use in future emission regulations. In the study reported in this paper, two latest-generation engines, one spark-ignited and the other compression-ignited, were used for a comparison of the particulate emission characteristics, including number density. Both engines were single-cylinder with the same displacement volume of 500 cm 3 , and neither included after-treatment traps or catalytic converters. Test fuels used for the study were: gasoline and E85 (mixture of 85% ethanol and 15% gasoline, sometimes called gasohol) for the spark-ignited engine having a compression ratio of 10; and ultralow sulfur diesel (ULSD) and BD100 (100% biodiesel, i.e. soybean methyl ester) for the compression-ignited engine having a compression ratio of 15. A fast-response particle spectrometer (DMS500) with heated sample line was used for continuous measurement of the particle size and number distribution in the size range of 5-1000 nm (aerodynamic diameter). The experimental results showed that particle number peaked within the range of 10-300 nm under all engine operating conditions, regardless of engine combustion type. An observed shift toward larger particle size with increasing engine load could be explained by particle coagulation. The effect of the different fuels on nanoparticle size distributions was dependent on the engine type (spark-ignition or compression-ignition).

Chemical Features of Particles Generated in an Ethylene/Ethanol Premixed Flame

“…26,27 When larger amounts of ethanol are added to the fuel mixture, ethanol pyrolysis prevails, leading to the formation of partially oxidized species, with the net effect of a reduction of the particle precursors and, lately, of the total mass of particulate matter. 4,28,29 It is worth noting that, also in the diffusioncontrolled conditions investigated at lab scale, the reducing effect of ethanol addition on the formation of the smaller size particles is overall less evident than the reduction of the total particulate matter. The concentration of the smaller size particles is not significantly reduced, and in some cases, it is even increased by the addition of ethanol.…”

“…Small amounts of ethanol added to the fuel enhance the pyrolysis of the fuel mixture because of the presence of oxygen-containing radicals deriving from ethanol decomposition. The larger production of ethylene and methyl radicals allows for the molecular growth pathways that lead to the formation of aromatics and soot. , When larger amounts of ethanol are added to the fuel mixture, ethanol pyrolysis prevails, leading to the formation of partially oxidized species, with the net effect of a reduction of the particle precursors and, lately, of the total mass of particulate matter. ,, It is worth noting that, also in the diffusion-controlled conditions investigated at lab scale, the reducing effect of ethanol addition on the formation of the smaller size particles is overall less evident than the reduction of the total particulate matter. The concentration of the smaller size particles is not significantly reduced, and in some cases, it is even increased by the addition of ethanol .…”

The effect of ethanol blending on mixture formation, combustion and soot emission studied in an optical DISI engine

“…In various research studies, ethanol blended fuels have shown reduced PM emissions in comparison to gasoline and its surrogate fuels [19][20][21] in DISI engines. However, there are also studies reporting increasing particulate concentration for gasoline engine fuels with higher ethanol content [22,23].…”

An Overview of the Influence of Biodiesel, Alcohols, and Various Oxygenated Additives on the Particulate Matter Emissions from Diesel Engines

“…Alcohols with longer carbon chain length have merit over shorter chain alcohols due to their higher calorific value, cetane number, improved miscibility with diesel, and superior cold flow properties [69,85]. The lower viscosity and density of alcohol blended fuels can improve the fuel atomization and fuel-air mixing consequently reducing the PM emissions [141][142][143]. A brief summary of observations made by different researchers for different alcohol fuels is presented in Table 2.…”