Cavitation, primary break-up and flash boiling of gasoline, iso-octane and n-pentane with a real-size optical direct-injection nozzle

Improvements to the direct-injection spark-ignition combustion system are necessary if the potential reductions in fuel consumption and emissions are to be fully realized in the near future. One critical link in the optimization process is the design and performance of the injectors used for fuel atomization. Multi-hole injectors have become the state-of-the-art choice for gasoline direct-injection engines due to their flexibility in fuel targeting by selection of the number and angle of the nozzle holes, as well as due to their demonstrated stability of performance under a wide range of operating conditions. Recently there has been increased attention devoted to the study of the flow through the internal passages of injectors because of the presence of particular fluid phenomena, such as large-scale vortical motion and cavitation patterns, which have been shown to influence the characteristics of primary break-up. Understanding how cavitation can be used to improve spray atomisation is essential for optimizing mixture preparation quality under early injection and stratified engine operating conditions but currently no data exist for injector-body temperatures representative of real engine operation, particularly at low-load conditions that can also lead to phase change due to fuel flash boiling. This paper outlines results from an experimental imaging investigation into the effects of fuel properties, temperature and pressure conditions on the extent of cavitation, flash boiling and, subsequently, primary break-up. This was achieved by the use of a real-size transparent nozzle of a gasoline injector from a modern direct-injection combustion system. Gasoline, iso-octane and n-pentane fuels were used at 20 and 90 °C injector-body temperatures for ambient pressures of 0.5 and 1.0 bar in order to simulate early homogeneous injection strategies for part-load and wide-open-throttle engine operation.     

Combustion characteristics of waste-oil produced biodiesel/diesel fuel blends

In this study, wasted cooking oil from restaurants was used to produce neat (pure) biodiesel through transesterification, and this converted biodiesel was then used to prepare biodiesel/diesel blends. The goal of this study was to compare the trace formation from the exhaust tail gas of a diesel engine when operated using the different fuel type: neat biodiesel, biodiesel/diesel blends, and normal diesel fuels. B20 produced the lowest CO concentration for all engine speeds. B50 produced higher CO₂ than other fuels for all engine speeds, except at 2000 rpm where B20 gave the highest. The biodiesel and biodiesel/diesel blend fuels produced higher NO_x for various engine speeds as expected. SO₂ formation not only showed an increasing trend with increased engine speed but also showed an increasing trend as the percentage of diesel increased in the fuels. Among the collected data, the PM concentrations from B100 engines were higher than from other fuelled engines for the tested engine speed and most biodiesel-contained fuels produced higher PM than the pure diesel fuel did. Overall, we may conclude that B20 and B50 are the optimum fuel blends. The species of trace formation in the biodiesel-contained fuelled engine exhaust were mainly C_nH_2n+2, DEP, and DPS. For the B100, B80, B50, and D fuelled engines, C₁₅H₃₂ was the dominant species for all engine speeds, while squalene (C₃₀H₅₀) was the dominant for B20. DEP was only observed in the B100, B80, and B50 fuelled engines in this study. The D fuelled engine showed a higher DPS production for engine speeds higher than 1200 rpm.     

Experimental study on particulate emission of a diesel engine fueled with blended ethanol–dodecanol–diesel

Experiments were conducted on a 4-cylinder direct-injection diesel engine which has a compressing ratio of 19, using ultra low sulfur diesel blended with ethanol using 1–1.5% by volume of 1-dodecanol as the solvent to investigate the particulate emissions of the engine under five engine loads and at engine speeds of 1800 and 2400 rev/min. Blended fuels containing 6.1%, 12.2%, 18.2% and 24.2% by volume of ethanol, corresponding to 2%, 4%, 6% and 8% by mass of oxygen in the blended fuel, were used. At both engine speeds, with an increase in ethanol in the fuel, the smoke opacity, the particulate mass concentration and the total number of nano-size particles are all reduced. A diesel oxidation catalyst (Finnkat) was used and found to further reduce particulate emission. The smoke opacity, the particulate mass concentration and the total number concentration at 2400 rev/min are higher than those at 1800 rev/min.     

Study of fuel consumption when introducing DME or ethanol into diesel engine

An investigation of the effect of DME or ethanol on fuel consumption is conducted in a four-stroke, one-cylinder, direct-injection diesel engine. DME or ethanol is first heated to pyrolyze and then the resultant product gas is introduced into air intake. Brake Specific Fuel Consumption (BSFC) can be reduced a lot, when emulsified fuel (diesel fuel emulsified with water) is fueled to diesel engine and DME is heated to about 1000 K before its being introduced into air intake. Results show that BSFC can be decreased by about 10% and diesel fuel consumption can be decreased by 18%. High saving rate of BSFC up to 10% is also acquired using ethanol instead of DME. To achieve high saving rate of BSFC, the heating temperature of about 1000 K is needed for DME operation, while the diesel engine exhaust temperature of about 750 K is enough for pyrolyzing ethanol. Hydrogen produced in DME or ethanol pyrolysis is considered as the main reason for the excellent fuel saving. The technique adopted in the present work is extremely easy to utilize, and may be firstly adopted on diesel engines for power plants, trains, ships, etc.     

Biodiesel production from tall oil with synthesized Mn and Ni based additives: Effects of the additives on fuel consumption and emissions

In this study, biodiesel fuel and fuel additives were produced from crude tall oil that is a by-product in the pulp manufacturing by craft or sulphate pulping process. Fatty acids and resinic acids were obtained from crude tall oil by distillation method. Tall oil methyl ester (biodiesel) was produced from fatty acids. Resinic acids were reacted with NiO and MnO₂ stoichiometrically for production of metallic fuel additives. Each metallic fuel additive was added at the rate of 8 μmol/l and 12 μmol/l to make mixtures of 60% tall oil methyl ester/40% diesel fuel (TE60) for preparing test fuels. Metallic fuel additives improved properties of biodiesel fuels, such as pour point and viscosity values. Biodiesel fuels were tested in an unmodified direct injection diesel engine at full load condition. Specific fuel consumption of biodiesel fuels increased by 6.00%, however, in comparison with TE60, it showed trend of decreasing with adding of additives. Exhaust emission profile of biodiesel fuels improved. CO emissions and smoke opacity decreased up to 64.28% and 30.91% respectively. Low NO_x emission was also observed in general for the biodiesel fuels.     

AEROSOL CHARACTERISATION IN MEDIUM-SPEED DIESEL ENGINES OPERATING WITH HEAVY FUEL OILS

Aerosol measurements were carried out in medium-speed diesel engines to determine the aerosol characteristics and formation in four-stroke diesel engines equipped with turbocharger(s) burning heavy fuel and high ash-content heavy fuel oil. The mass size distributions are bimodal with a main mode at 60–90 nm and a second mode at 7–10 μm. The small mode particles are formed by nucleation of volatilized fuel oil ash species, which further grow by condensation and agglomeration. The large mode particles are mainly agglomerates of different sizes consisting of the small particles. The number size distributions peak at 40–60 nm, as also observed in the SEM micrographs. Agglomerates consisting of these primary spherical particles are also found. The TEM micrographs reveal that these particles consist of even smaller structures. Based on the mass and elemental size distributions evidence of high volatility of the fuel oil ash was found. The main effect on the aerosol size distributions was caused by the engine type and fuel oil properties.     

Experimental study on performance and emissions of a high speed diesel engine fuelled with n-butanol diesel blends under premixed low temperature combustion

In the present paper, results of an experimental investigation carried out in a modern diesel engine running at different operative conditions and fuelled with blends of diesel and n-butanol, are reported. The exploration strategy was focused on the management of the timing and injection pressure to achieve a condition in which the whole amount of fuel was delivered before ignition. The aim of the paper was to evaluate the potential to employ fuel blends having low cetane number and high resistance to auto-ignition to reduce engine out emissions of NOx and smoke without significant penalty on engine performance. Fuel blends were mixed by the baseline diesel (BU00) with 20% and 40% of n-butanol by volume. The n-butanol was taken by commercial production that is largely produced through petrochemical pathways although the molecule is substantially unchanged for butanol produced through biological mechanisms.The experimental activity was performed on a turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system. The engine equipment includes an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injectors. Engine tests were carried out at 2500 rpm and 0.8 MPa of BMEP exploring the effect of start of injection, O₂ concentration at intake and injection pressure on combustion behavior and engine out emissions. The in-cylinder pressure and rate of heat release were investigated for the neat diesel and the two blends to evaluate engine performance and exhaust emissions both for the conventional diesel and the advanced premixed combustion processes.The management of injection pressure, O₂ concentration at intake and injection timing allowed to realize a partial premixed combustion by extending the ignition delay, particularly for blends. The main results of the investigation made reach smoke and NOx emissions due to the longer ignition delay and a better mixing control before combustion. The joint effect of higher resistance to auto ignition and higher volatility of n-butanol blends improved emissions compared to the neat diesel fuel with a low penalty on fuel consumption.     

Experimental investigation on particulate emissions of a direct injection diesel engine fueled with diesel–diethyl adipate blends

Euro V diesel fuel blended with 8.1%, 16.4%, 25% and 33.8% by volume of diethyl adipate (DEA), corresponding to 3%, 6%, 9% and 12% by mass of oxygen in the blended fuels, were tested on a 4-cylinder direct-injection diesel engine. Experiments were conducted under five engine loads at a steady speed of 1800 rev/min to investigate the effects of the blended fuels on combustion and particulate emission characteristics. The results indicate an increase in ignition delay and the amount of heat release in the premixed burning phase, while a decrease in both diffusive and total combustion duration with an increase in DEA in the fuel. Compared to the diesel fuel, the particulate mass concentration and the total number of particles are reduced significantly, whereas the proportion of soluble organic fraction (SOF) in the particles increases with increasing DEA in the fuel. The increase in SOF might increase the toxicity of the particles. Moreover, the geometric mean diameter (GMD) of the particles shifts towards smaller size. A diesel oxidation catalyst was used and found to further reduce both particulate mass and total number concentration. The results also show that the DOC could reduce the finer particles more effectively.     

The effects of fuel characteristics and engine operating conditions on the elemental composition of emissions from heavy duty diesel buses

The effects of fuel characteristics and engine operating conditions on elemental composition of emissions from twelve heavy duty diesel buses have been investigated. Two types of diesel fuels – low sulfur diesel (LSD) and ultra low sulfur diesel (ULSD) fuels with 500 ppm and 50 ppm sulfur contents respectively and 3 driving modes corresponding to 25%, 50% and 100% power were used. Elements present in the tailpipe emissions were quantified by inductively coupled plasma mass spectrometry (ICPMS) and those found in measurable quantities included Mg, Ca, Cr, Fe, Cu, Zn, Ti, Ni, Pb, Be, P, Se, Ti and Ge. Multivariate analyses using multi-criteria decision making methods (MCDM), principal component analysis (PCA) and partial least squares (PLS) facilitated the extraction of information about the structure of the data. MCDM showed that the emissions of the elements were strongly influenced by the engine driving conditions while the PCA loadings plots showed that the emission factors of the elements were correlated with those of other pollutants such as particle number, total suspended particles, CO, CO₂ and NO_x. Partial least square analysis revealed that the emission factors of the elements were strongly dependent on the fuel parameters such as the fuel sulfur content, fuel density, distillation point and cetane index. Strong correlations were also observed between these pollutants and the engine power or exhaust temperature. The study provides insights into the possible role of fuel sulfur content in the emission of inorganic elements from heavy duty diesel vehicles.     

On-road and laboratory evaluation of combustion aerosols—Part1: Summary of diesel engine results

The objective was to characterize diesel exhaust aerosols on road and to duplicate the results in the laboratory without altering the physical characteristics of the nuclei mode. On-road emissions from four, heavy-duty diesel truck engines were measured. The same engines were reevaluated in the manufacturers’ laboratories. For highway cruise and acceleration conditions, all engines produced bimodal size distributions with the nuclei mode ranging in size from 6 to 11 nm and the accumulation mode from 52 to 62 nm. On-road size distribution measurements nearly always showed a nuclei mode while laboratory measurements showed a nuclei mode under many, but not all conditions. Laboratory studies showed that nuclei mode particles consisted mainly of heavy hydrocarbons. More than 97% of the volume of 12 and 30 nm particles disappeared on heating to 400 °C. The volatility resembled that of C24–C32 n-alkanes implying a significant contribution from lubricating oil.     

Diesel and bio-diesel fuel deposits on a hot surface

The aim of this study is to investigate the deposition remains of fuel droplets that impinge on a hot surface of Aluminum Alloy. The fuel droplets tested are diesel fuel (DF) and palm oil based ester that refers as a bio-diesel fuel (BDF). Temperatures of Aluminum Alloy surface and impingement interval of droplets are two parameters that were considered for various conditions of experiments. The maximum evaporation point (MEP) obtained from evaporation characteristics for each fuel was used as a reference point to decide the surface temperature of the Aluminum Alloy, where deposits of fuel were observed. The impingement interval was set at 3, 5 and 8 s with various surface temperatures of 320 °C and 370 °C. To understand the effect of heat transfer on deposition development, surface temperature of deposits was measured by using infrared thermometer. The deposition development depended on a few factors such as droplet impingement interval, hot surface temperature, type of fuel, and heat transfer of fuel deposits. BDF produced rapid development of fuel deposits comparing to DF.     

Microwave-heated pyrolysis of waste automotive engine oil: Influence of operation parameters on the yield,composition, and fuel properties of pyrolysis oil

The pyrolysis of waste automotive engine oil was investigated using microwave energy as the heat source, and the yield and characteristics of the pyrolysis oils (i.e. elemental analysis, hydrocarbon composition, and potential fuel properties) are presented and discussed. The microwave-heated pyrolysis generated an 88 wt.% yield of condensable pyrolysis oil with fuel properties (e.g. density, calorific value) comparable to traditional liquid transportation fuels derived from fossil fuel. Examination of the composition of the oils showed the formation of light aliphatic and aromatic hydrocarbons that could also be used as a chemical feedstock. The oil product showed significantly high recovery (90%) of the energy present in the waste oil, and is also relatively contaminant free with low levels of sulphur, oxygen, and toxic PAH compounds. The high yield of pyrolysis oil can be attributed to the unique heating mode and chemical environment present during microwave-heated pyrolysis. This study extends existing findings on the effects of pyrolysis process conditions on the overall yield and formation of the recovered oils, by demonstrating that feed injection rate, flow rate of purge-gas, and heating source influence the concentration and the molecular nature of the different hydrocarbons formed in the pyrolysis oils. The microwave-heated pyrolysis can be performed in a continuous operation, and the apparatus described which is fitted with magnetrons capable of delivering 5 kW of microwave power is capable of treating waste oil at a feed rate of 5 kg/h with a positive energy ratio of 8 (energy content of hydrocarbon products/electrical energy supplied for microwave heating) and a net energy output of 179,390 kJ/h. Our results indicate that microwave-heated pyrolysis shows exceptional promise as a means for recycling and treating problematic waste oil.     

Effect of injection and ignition timings on performance and emissions from a spark-ignition engine fueled with methanol

Optimal injection and ignition timings and the effects of injection and ignition timings on performance and emissions from a high-compression direct-injection stratified charge spark-ignition methanol engine have been investigated experimentally. The results have shown that direct-injection spark-ignition methanol engine, in which a non-uniform mixture with a stratified distribution can be formed, has optimal injection and ignition timings to obtain a good combustion and low exhaust emissions in the overall mode range. Both methanol injection timing and ignition timing have a significant effect on methanol engine performance, combustion, and exhaust emissions. At an engine speed of 1600 rpm, full load, and optimal injection and ignition timings, methanol engine can obtain shorter ignition delay, lesser cycle-by-cycle variation, the maximum in-cylinder pressure, the maximum heat release rate, and higher thermal efficiency compared to the case of non-optimized injection and ignition timings. For methanol engine, the optimization of injection timing and ignition timing can lead to an improvement of brake-specific fuel consumption of more than 10% compared to non-optimized case in the overall load range and engine speed of 1600 rpm. The best compromise between thermal efficiency and exhaust emissions is reached at optimal injection and ignition timings.     

Production of lower alkenes and light fuels by gas phase oxidative cracking of heavy hydrocarbons

The gas phase oxidative cracking (GOC) and non-oxidative pyrolysis of heavy hydrocarbons were investigated, with decalin (decahydronaphthalene) and tetralin (tetrahydronaphthalene) as the model compounds for naphthenic hydrocarbon and aromatic hydrocarbon, respectively. Unlike pyrolysis, the ring rupture of decalin or tetralin molecule and the decoking ability of system were significantly enhanced due to the introduction of O₂ in GOC. For GOC of decalin, both the lower alkenes and the light fuels were obtained. At lower temperatures the light fuels mainly contained alkyl benzene, alkyl cyclohexane and isoparaffins, while it was rich in BTX (benzene, toluene and xylenes) at higher temperatures. A 38.9% yield of lower alkenes and 48.0% yield of light fuels (BTX mass content: 59.9%) at 100% decalin conversion were obtained under the conditions of 800 °C and decalin / O₂ = 0.5. For GOC of tetralin, both the dehydrogenation and the cracking reactions dominated the reaction routes, resulting in a high mass content of alkyl naphthalene and alkyl benzene in the light fuels. The estimation of O₂ distribution in the products demonstrated that O₂ participated primarily in the oxydehydrogenation reactions at low temperatures, while mainly in the partial oxidation reactions at high temperatures to produce CO_x (x = 1, 2).     

Effects of diesel particulate trap and addition of di-methoxy-methane,di-methoxy-propane to diesel on emission characteristics of a diesel engine

The objective of this investigation was to improve the performance of a diesel engine by adding oxygenated fuel additives of known percentages. The fuel additives di-methoxy-methane (DMM) and di-methoxy-propane (DMP) were separately blended with diesel fuel in proportions of 1 ml, 3 ml and 5 ml. The experimental study was carried out on a single cylinder DI diesel engine. The result showed an appreciable reduction of emissions such as smoke density, particulate matter and marginal increase in the performance when compared with normal diesel run. The same engine was employed with diesel particulate trap (DPT) in the exhaust pipe to study its influence on the emission analysis.     

Antioxidative efficiency of novel β-naphthol derivatives in storage assays of cracked naphtha

The types of hydrocarbons found in gasoline have great influence on the formation of gum (nonvolatile, insoluble, adhesive resin that forms sediments within fuel systems of an engine). In this study, the synthetic compound β-naphthol has been used in order to generate novel antioxidative substances: AO1 [6-N-ethyl,N-ethylamino)β-naphthol], AO2 [6-N-ethyl,N-diethylamino)-β-naphthol] and AO3 [mixture of amino-β-naphthol and 1,6-di-amino-β-naphthol]. The derived compounds were subjected to accelerated oxidative stability assays [potential gum (PG) and induction period (IP)] and to storage assays [washed gum (WG) and ASTM color] during six months with cracked naphtha provided by the petroleum refinery RPBC (Presidente Bernardes Refinery, in Cubatão, Brazil). During the PG and IP assays, the experimental amine mixture AO3 and the commercial product known as PDE were highlighted as good oxidation inhibitors, yielding average values of 39.15 mg/100 ml and 637 min, respectively. After the storage period, a better antioxidant behavior was observed for the experimental compound AO2, which provided an average WG value of 6.1 mg/100 ml.     

Macroscopic diesel fuel spray shadowgraphy using high speed digital imaging in a high pressure cell

Spray formation from diesel fuel injection through a realistic heavy-duty multi-hole common rail injector is studied in a newly developed high pressure, high temperature cell, using digital high speed shadowgraphy at 4500 frames per second. Care is taken to establish accurate synchronisation between camera and injection system and because of the relatively large exposure time, an effective camera image time is calculated for every frame. Further emphasis is given to determining the actual start of fuel mass injection by comparing (for each injection) a predetermined, rail pressure dependent needle relaxation distance to the actual needle lift signal. The spatiotemporal evolution of the spray is found to reproduce well in general, but often sprays suffer from short-lived, small, laterally moving anomalies, which influence axial motion and the spray cone angle. High speed shadowgraphy allows this to be observed and taken into account. After an overview of methods found in the literature, an algorithm for geometrical analysis is presented, which is based on an extension of a combination of those methods. In this algorithm, a local spray angle ϑ_i(x) is determined from lateral cross-sections at 80% of the shadow level in order to encompass most of the spray without being too sensitive to background noise. The macroscopic cone angle ϑ_cone is derived from the approximate constancy of ϑ_i(x) over a relatively long axial distance. Spray penetration is obtained by lateral integration of the spray shadow. A procedure for accurate correlation of spray growth with time shows that the growth is proportional to t^b with b = 0.57 ± 0.02 for a common rail pressure of 150 MPa and a gas density 33 kg/m³ (N₂ at room temperature). The exact value of b is very sensitive to uncertainties in synchronisation and the start of injection determination. The spray cone angle ϑ_cone is not constant, but varies with time during an injection, mainly as a result of spray shape changes.     

The effects of vegetable oil properties on injection and combustion in two different diesel engines

Four different vegetable oils, each in at least 3 different stages of processing, have been characterized according to their physical and chemical properties, their injection and atomization characteristics, and their performance and combustion characteristics in both a direct-injection and an indirect-injection diesel engine. The injection and atomization characteristics of the vegetable oils are significantly different than those of petroleum-derived diesel fuels, mainly as the result of their high viscosities. Heating the oils, however, results in spray characteristics more like those observed with diesel fuel. The 2 engine types demonstrated different sensitivities to the composition of the various oils. The combustion characteristics and the durability of the direct-injection engine were affected by the oil composition. The indirect-injection engine, however, was not greatly affected by composition. Two different preliminary specifications have been proposed: a stringent specification including compositional requirements for direct-injection engines, and a less stringent specification for indirect-injection engines. The specifications are discussed in terms of the data and the rationale used in their development. Some precautions concerning the application of the specifications are also presented. Presented at the AOCS Annual Meeting in Chicago, May 1983.     

TEM study on volatility and potential presence of solid cores in nucleation mode particles from diesel powered passenger cars

Nucleation mode particles were investigated for their morphology using TEM and the presence or absence of solid cores was addressed. At cold start idle nucleation particles were observed in the exhaust of a diesel passenger car. These particles occurred with both low and high S fuel and were only partly volatile in a thermodenuder, which indicates that the composition was not sulfate and as derived from TEM/EDX (transmission electron microscopy/energy dispersive X-ray analysis) probably not ash. It could be high boiling hydrocarbons, or primary soot particles. With all fuels at warm idle no nucleation particles and only soot particles were observed in the SMPS and the TEM. With 3.0×10¹¹ s^?1 the total soot particle number during idle was much less than during driving, e.g. at 120 km h^?1 the emission rate was 6.7×10¹² s^?1.At high load and high S fuel 10–20 nm nucleation particles were observed by SMPS and TEM. A thermodenuder at 280 °C and TEM showed that all nucleation particles were volatile. EDX gave a weak S-signal only. Some nucleation particles contained smaller spots (1–3 nm) with a very high contrast, which might be due to heavy elements. However, under the electron beam of the TEM these spots disappeared and EDX analysis was not possible. With low S fuel at 120 km h^?1 only soot particles and no nucleation particles were observed.     

Optimization of a natural gas SI engine employing EGR strategy using a two-zone combustion model

Natural gas has been recently used as an alternative to conventional fuels in order to satisfy some environmental and economical concerns. In this study, a natural gas spark-ignition engine employing cooled exhaust gas recirculation (EGR) strategy in a high pressure inlet condition was optimized. Both engine compression ratio and start of combustion timing were optimized in order to obtain the lowest fuel consumption accompanied with high power and low emissions. That was achieved numerically by developing a computer simulation of the four-stroke spark-ignition natural gas engine. A two-zone combustion model was developed to simulate the in-cylinder conditions during combustion. A kinetic model based on the extended Zeldovich mechanism was also developed in order to predict NO emission. In addition, a knocking model was incorporated with the two-zone combustion model in order to predict any auto-ignition that might occur. It was found that the value of the compression ratio at which the minimum fuel consumption occurs varies with the engine speed. A minimum fuel consumption of about 200 g/kW h was achieved at an engine speed of 1500 rpm, inlet conditions of 200 kPa and 333 K, and a compression ratio of about 12. Also, it was found that cooled EGR can significantly reduce NO emission at high compression ratio conditions. NO emission decreased by about 28% when EGR was increased from 20% at compression ratio of 10 to 27% at compression of 12 at the same engine speed of 3000 rpm.