The objective of reducing the pollutant emissions and in particular those of particles has motivated researchers to explore alternative fuels to replace the conventional fossil ones. It is well known from literature the contribution of spark ignition (SI) engines to the emission of particles too [1]. Among the liquid biofuels for SI engines, pure and blended alcohols are recommended due to their low sooting tendency as well pointed out by study involving optical diagnostics of combustion process [2]. Gaseous fuels, as compressed natural gas (CNG), have the advantage over liquid fuels of reducing particle emissions thanks to their lower carbon content. In this case, particle formation depends on the gas components concentration which can vary with geographical source, time of year, and treatments applied [3]. Although the strong reduction of particles when gaseous fuels are used, their concentration at exhaust still cannot be considered negligible. Their presence can be attributed to the lubricant oil that participates to the combustion. Hydrogen fuel could have great potentiality to diminish the particle emissions due to the absence of carbon atoms in its molecule. Nevertheless, lubricant oil can play an important role on particle emissions. This study aims to provide a better insight on the effect of oil on the particle emissions at exhaust of small displacement SI engines equipped with direct (DI) and port fuel injection (PFI) systems fueled with commercial gasoline (G) and gaseous fuels, both CNG and hydrogen. A methodology able to evaluate the oil contribution was developed considering several percentage of oil to simulate in the medium and late time oil effect [4]. Fig. 1 shows the percentage of particles emitted from CNG, GPFI and GDI at different oil content. The particle emissions are classified in particles smaller than 23 nm which will be likely subject to the next emission regulation and those larger than 23 nm actually regulated. Oil addition produces a significant increase of particle emissions whatever the fuel and the engine configuration. The different proportion between the two range classes of the particles depends on the role played by the nucleation and agglomeration processes. Generally, the higher volatility species of the oil tend to nucleate contributing to the formation of sub-23 nm particles. On the other hand, the heavier organic components are more prone to condense on existing particles resulting in more pronounced accumulation mode. The effect of oil is also evident for H2 fueled engine as reported in Fig 2. A large number of sub-23 nm particles was measured at the engine conditions characterized by a more oil consumption as high engine speed and low load. These results highlighted the significant role played by the lube oil on particles emitted from gaseous fueled engines, and the necessity to improve its quality to reduce their impact on the atmosphere and then improve the urban air quality.
Role of lubricant oil on particle emissions from a PFI/DI SI engines powered with gaseous fuels
F Catapano;S Di Iorio;A Magno;P Sementa;BM Vaglieco
2022
Abstract
The objective of reducing the pollutant emissions and in particular those of particles has motivated researchers to explore alternative fuels to replace the conventional fossil ones. It is well known from literature the contribution of spark ignition (SI) engines to the emission of particles too [1]. Among the liquid biofuels for SI engines, pure and blended alcohols are recommended due to their low sooting tendency as well pointed out by study involving optical diagnostics of combustion process [2]. Gaseous fuels, as compressed natural gas (CNG), have the advantage over liquid fuels of reducing particle emissions thanks to their lower carbon content. In this case, particle formation depends on the gas components concentration which can vary with geographical source, time of year, and treatments applied [3]. Although the strong reduction of particles when gaseous fuels are used, their concentration at exhaust still cannot be considered negligible. Their presence can be attributed to the lubricant oil that participates to the combustion. Hydrogen fuel could have great potentiality to diminish the particle emissions due to the absence of carbon atoms in its molecule. Nevertheless, lubricant oil can play an important role on particle emissions. This study aims to provide a better insight on the effect of oil on the particle emissions at exhaust of small displacement SI engines equipped with direct (DI) and port fuel injection (PFI) systems fueled with commercial gasoline (G) and gaseous fuels, both CNG and hydrogen. A methodology able to evaluate the oil contribution was developed considering several percentage of oil to simulate in the medium and late time oil effect [4]. Fig. 1 shows the percentage of particles emitted from CNG, GPFI and GDI at different oil content. The particle emissions are classified in particles smaller than 23 nm which will be likely subject to the next emission regulation and those larger than 23 nm actually regulated. Oil addition produces a significant increase of particle emissions whatever the fuel and the engine configuration. The different proportion between the two range classes of the particles depends on the role played by the nucleation and agglomeration processes. Generally, the higher volatility species of the oil tend to nucleate contributing to the formation of sub-23 nm particles. On the other hand, the heavier organic components are more prone to condense on existing particles resulting in more pronounced accumulation mode. The effect of oil is also evident for H2 fueled engine as reported in Fig 2. A large number of sub-23 nm particles was measured at the engine conditions characterized by a more oil consumption as high engine speed and low load. These results highlighted the significant role played by the lube oil on particles emitted from gaseous fueled engines, and the necessity to improve its quality to reduce their impact on the atmosphere and then improve the urban air quality.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
