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Low-speed pre-ignition (LSPI) remains one of the challenges of Direct Injection (DI) Spark Ignition (SI) engines due to its potential to induce a heavy knock. Several mechanisms have been identified in the literature as plausible causes for LSPI. The physical and chemical properties of lubricant oils play a role on some of these causes. The present work aims at getting an independent procedure to determine the proneness of lubricant oils to ignite. To this end, the ignition delay (ID) of different oil formulations is experimentally determined in a constant-pressure flow facility through two different optical techniques: Schlieren and OH* chemiluminescence imaging. The investigation explores the effect of base-stock formulation, oil specification quality level, different additive types content, aging, and oxidation on oil reactivity for several thermodynamic conditions. Differences in ignition delay were found among base stocks, correlating with the American Petroleum Institute (API) group classification. However, no significant differences were found among additive packages previously reported to yield different LSPI occurrences. Hence, differences in reactivity among lubricating oil formulations are not the determining factor explaining their different LSPI occurrences in an engine. Similarly, specific lubricant additive content, aging, and oxidation do not importantly modify the measured ignition delay.

[EN] One source of low-speed pre-ignition in turbocharged gasoline direct injection engines is the presence of oil droplets in the combustion chamber. In this study, oil droplets released due to the piston reciprocating motion, have been quantified as function of oil viscosity and engine speed, by means of a motored test rig under ambient pressure conditions. Oil droplets were collected using a sandwich-like support and absorbing paper. An image processing methodology was developed to identify critical regions of the piston prone to the appearance of oil. Results show that oil is scrapped by the piston rings and released to the combustion chamber in zones transverse to the piston pin, at speeds as low as 500 rpm. Oil viscosity does not have a determining effect on the oil amount reaching the combustion chamber, while engine speed greatly increases this phenomenon, with a critical point at 2500 rpm and oil temperature of 80 degrees C., Author Sophia Bastidas would like to thank the support of the program Ayudas de Investigacion y Desarrollo (PAID-01-17) of the Universitat Politecnica de Valencia.

Utilization of natural gas fuels in heavy duty vehicles offers an effective solution to reduce global warming and improve urban air quality. However, there are problems related to catalyst durability and release of unburned methane (methane slip). Catalyst durability can be achieved through clever designs of both catalyst material and its regeneration process. In this paper, we studied extensively low temperature regeneration strategies of a commercial methane oxidation catalyst (MOC), a three-way catalyst (TWC) and a diesel oxidation catalyst (DOC) as well as two coupled catalysts; TWC-MOC and DOC-MOC. Methane and propane conversion along with NO2, NO, SO2, CO, N2O and NH3 formation were recorded and analyzed in a laboratory setup using a FTIR multigas analyzer. According to our findings, the MOC and the DOC can be regenerated under a broader range of O2 concentrations whereas the TWC requires a very low O2 concentration or anoxic conditions for efficient regeneration. The conversion increase ranged between 0 and 20 percentage points for methane and 0–45 percentage points for propane depending on the catalyst and regeneration technique. The coupled catalysts were highly effective in methane conversion and possessed higher tolerance against SO2 poisoning compared to single catalysts. The study further revealed that 10 ppm regulation limit of NH3 emission is plausible to exceed during the regeneration of a catalyst. By controlling the exhaust gas composition during the regeneration and length of the regeneration, the NH3 and N2O emissions can be minimized.

There is an increasing interest in reducing CO2 as far as it is the main responsible of greenhouse gas (GHG) emissions. Since the contribution of heavy-duty (HD) vehicles to GHG emissions of the road transport sector reaches 24% in the European Union, Liquefied Petroleum Gas (LPG) is suggested as a promising alternative fuel to be introduced in HD vehicles. The main drawback when using LPG in diesel engines is its poor autoignition behavior. To overcome this difficulty is possible to mix LPG with Hydrotreated Vegetable Oil (HVO) or diesel fuel, which acts as an ignition improver. This work has focused on LPG-HVO blends up to 75 %m/m LPG content, with lower LPG content admixtures included. Another measure to promote autoignition is using advanced injection strategies, particularly at low thermal conditions in the combustion chamber. This study concluded that 25LPG-75HVO blend (without any injection strategy modification) and 50LPG-50HVO blend (with advanced injection strategy) show better autoignition behavior than diesel fuel at low thermal conditions. At usual combustion conditions, LPG-HVO blends up to 75 %m/m LPG content can be supplied using an advanced injection strategy, and achieving similar autoignition behavior than diesel. LPG and HVO contents in the blend can be balanced depending on the thermal conditions. Therefore, a novel injection system with an in-line mixing valve capable of managing the instantaneous LPG/HVO ratio for compression ignition engines, is suggested. Testing these blends with advanced injection strategies using the in-line mixing system in a real HD engine would confirm these results.

Wall flow–type particulate filters are used in diesel vehicle engines to reduce particulate emissions below the limits established in regulations Euro 5 and Euro 6. The soot accumulated in the trap is eliminated during regeneration processes, often combining passive strategies with active ones. Active regeneration is conducted by modifications of the engine control parameters with respect to those set for normal vehicle operation. In this work, three of these parameters were modified to look for an optimized regeneration strategy, considering fuel consumption, gaseous emissions and rate of regeneration. The selected parameters were injection timing (affecting all injection events), exhaust gas recirculation and amount of postinjected fuel. The fuel tested was considered as an additional variable, and therefore, tests were performed with three different fuels: an ultra-low sulfur diesel fuel, a biodiesel fuel produced from animal fat and a gas-to-liquid fuel from low-temperature Fischer–Tropsch process. It...

Particulate filters are massively used in new diesel vehicles to reduce particulate emissions below the regulation limits. The setting of filters in the exhaust lines imposes various changes in the engine working conditions, including increased back-pressure, resulting in some fuel penalty. In this work, the filter loading process was investigated in a modern common-rail diesel engine equipped with diesel oxidation catalyst and diesel particulate filter. The engine was fuelled with EN-590 diesel fuel and run in a highly emissive operating mode selected among those reproducing the New European Driving Cycle. During the test the intake/exhaust conditions, intake charge, injection and combustion timing, fuel consumption and regulated emissions were measured. It was observed that the EGR (exhaust gas recirculation) ratio decreased from 30% down to 21%, shifting the combustion process away from its design parameters. In consequence, nitrogen oxides emissions increased around 60% along the test, compromising the objectives of the emission regulations. A 4% increase in fuel consumption throughout the test was measured, this value being higher than that expected from previous literature. An energy balance revealed that such penalty was caused by increased pumping losses and, especially, by higher energy losses via exhaust gas temperature and engine coolant.

An automotive diesel engine was tested in three representative modes of soot accumulation, active regeneration and spontaneous regeneration of its catalyzed diesel particulate filter (DPF), among the typical driving operation modes. During the engine tests, pressure and temperature along the DPF were measured, and soot samples were taken from the exhaust manifold upstream of the DPF for their thermal, structural and morphological characterization. The collected soot samples were subjected to: Transmission Electron Microscopy (TEM) for morphological analysis, thermal heating under oxidant atmosphere for studying the oxidation kinetics, Raman spectroscopy for describing their nanostructure and X-ray diffraction spectroscopy (XRD) for studying their internal lattice parameters. When the engine was operated in a typical accumulation mode, the pressure drop across the DPF increased up to 80 hPa with diesel fuel, while pressure drop stopped increasing after 4000 s of engine testing with biodiesel. In the regeneration mode, the DPF regenerated more slowly in the biodiesel case as a consequence of lower post-injected fuel energy and thus lower exhaust temperature. In the self-regenerating mode, the DPF was charged more slowly with biodiesel than with diesel fuel and its break even temperature was 40 °C lower with biodiesel fuel. These results provide further evidence that biodiesel soot is more reactive to oxidation. Although thermogravimetric results confirmed this tendency based on the differences on the pre-exponential factor, Raman spectra showed that biodiesel soot reached more ordered graphite-like structures and lower amorphous carbon concentration and XRD analysis showed that biodiesel soot displayed a higher degree of graphitization. The TEM analysis of the agglomerates showed that soot primary particles obtained with biodiesel fuel were significantly smaller and had higher specific active surface than those of diesel soot. From these results, an interpretation of the differences in soot oxidation between both soot samples was made based on the different length scales, from the carbon fringes to the particulate filter.

Raman analysis of carbonaceous materials requires selecting a number of parameters, some of which alter the sample and affect the resulting spectra. Much literature has discussed about the most appropriate values of these parameters for analyzing graphite, coals, or more disordered materials, but no published studies have proposed appropriate values for comparing soot derived from diesel engines fueled with different fuels. This comparison is essential for the design of the regenerative diesel particulate traps that all new automotive diesel engines must incorporate. The effect of three Raman parameters was studied over the same spot to eliminate dispersions associated with the heterogeneity of the sample: laser wavelength, intensity of the incident laser, and exposure time. Among the tested laser wavelengths, 488 nm was preferred for comparing soot samples because it maximized the difference between their spectra due to better signal-to-noise ratio. The selection of the incident laser power is limited by...

A thermogravimetric analyzer (TGA) was used to oxidize real diesel soot produced in a modern four-cylinder, turbo-charged, diesel engine equipped with a common rail injection system. In the first p...

Biodiesel from different mixtures of animal fat and soybean oil has been synthesized, and its properties have been evaluated and related to its composition. A mixture of 50 vol % of both raw materials has been selected as a suitable feedstock for industrial biodiesel production, and a computer simulation of the production process using Aspen Plus software has been carried out to evaluate the industrial feasibility of this scheme using this cheaper feedstock. The results obtained suggest that the process proposed and described produces a biodiesel with the selected feedstock acceptable by the standards with a lower final cost. The feedstocks employed are cheaper and consist of a waste fat without any other use, thus increasing the environmental benefits of the biodiesel and reducing dependency on conventional agricultural raw materials.

Biofuels composed by fatty acid methyl esters are widely used as partly substituting fuels for diesel fossil fuels. Additionally, it is expected that the diesel biofuel norms will be extended to ethyl esters produced from bioethanol in the upcoming years. A precise knowledge of the standard enthalpy of formation is necessary for the calculation of some parameters useful for the analysis of the combustion process and emissions of a diesel engine operating with different fuels, such as the heating value, the adiabatic flame temperature or the kinetic mechanisms. However, experimental data for this property are scarce, and only available for short-chain, saturated methyl esters. In this work, four estimation methods for the calculation of the enthalpy of formation are examined and compared. Three of them are simple methods based on groups or bonds contribution, and another one is a computational method (with Gaussian 03 software). After presenting the implementation rules for each of them, conclusions are stated based on the results attained. Gaussian and Benson-Groups methods seem to be more accurate in predicting the actual values of the enthalpy of formation, both methods considering the separation between double bonds and the edge effects in the molecule. However, only the Gaussian method considers the effect of the position of the double bond in the molecule for all the unsaturated esters.