Journal of Energy Engineering

Hydrotreated vegetable or waste cooking oils (HVOs or HWCOs) are considered second-generation biofuels and are regarded as a promising alternative to current market diesel because they mainly consist of paraffinic hydrocarbons. This paper presents an experimental investigation conducted in order to examine the potential of HWCO as a substitute of diesel fuel. The HWCO used was produced from waste cooking oils through a catalytic hydrotreatment process. The main target of the study was the investigation of the emissions and combustion characteristics of the HWCO in comparison with conventional diesel. To that aim, a light-duty common-rail Euro 5 diesel engine, running on neat HWCO, was tested over the New European Driving Cycle (NEDC) at the engine test bed. The results showed lower ${\mathrm{CO}}_2$, CO, and hydrocarbon emissions, but increased ${\mathrm{NO}}_x$ emissions. Combustion analysis, performed at specific steady-state operating points, revealed the differences in the combustion mechanism between HWCO and market diesel, forming a basis for the interpretation of emissions results.

The gasification of wood allows the production of wood gas, which can be used as an energy source in large spark-ignition (SI) piston engines located in agricultural areas for generating electric power. The composition of wood gas depends on the fuel source and the processing technique. The primary objective of this paper is to investigate the main performance and emission characteristics of a multicylinder, four-stroke, turbocharged, spark-ignited engine fueled with three different types of wood gas at various air to fuel excess ratios. This engine is used for electricity production especially in small generator sets. In order to examine the effect of wood-gas composition on performance and exhaust emissions, a theoretical investigation is conducted by using a comprehensive two-zone phenomenological model. The results concern some of the main engine performance characteristics, i.e., brake specific fuel consumption and maximum cylinder pressure, and specific NO and CO emissions. The predictive ability of the model has been tested against experimental measurements. The results of simulation are found to be in good agreement with the variation trends of the experimental data with engine load. The conclusions from this investigation are valuable for the use of wood gas as a full supplement energy source in a heavy-duty, spark-ignited engine used for electric power generation in agriculture areas, where the composition of the produced wood gas is not fixed but depends on the fuel feedstock source and the type of gasification.

The present work evaluates the effects of using blends of diesel fuel with two (straight) vegetable oils, viz sunflower and cottonseed, and their corresponding methyl ester biodiesels in proportions of 10% and 20% (by volume), on the performance and emissions of a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy-duty direct injection (HDDI), Mercedes-Benz, bus diesel engine. The series of tests are conducted using each of the biofuels blends, with the engine working at (the same) three loads and two speeds, with measurements taken of fuel consumption and exhaust regulated emissions, i.e., smoke, nitrogen oxides (${\mathrm{NO}}_{\mathrm{x}}$), carbon monoxide (CO), and total unburned hydrocarbons (HC). Results of heat release combustion analysis of experimentally obtained cylinder pressure diagrams, together with the differing physical and chemical properties of these biofuels against those for the diesel fuel, which constitutes the baseline fuel, aid the correct interpretation of the observed engine behavior. With increasing percentage of all biofuels in the blends, reduction of smoke opacity (higher for the cottonseed oil or its biodiesel against their sunflower counterparts) is observed, slight increase of ${\mathrm{NO}}_{\mathrm{x}}$, increase of HC emissions, increase of CO with the vegetable oil blends, and decrease with the biodiesel ones, while brake thermal efficiency remains practically the same.

The objective of this study was to examine key gasoline properties, such as octane rating and volatility of ternary blends with ethanol and ethyl-tert-butyl-ether (ETBE). Ethanol and ETBE were added in various concentrations in specific refinery gasoline pool components, so a total of 30 gasoline-ethanol-ETBE samples were prepared and tested. Vapor pressure and octane numbers [research octane number (RON) and motor octane number (MON)] were determined for the mixtures containing 0.9–5.5% v/v ethanol and 2.0–9.8% v/v ETBE. Ethanol was always considered a valuable component for refinery gasoline pool due to its good antiknock characteristics. However, its azeotropic behavior in gasoline is considered as a drawback for the vapor pressure of the blend. On the other hand, the use of ETBE in gasoline increases the octane number and lowers the vapor pressure, thus allowing refinery blenders to use a higher vapor pressure base gasoline in the final fuel formulation. Experimental results indicated that ethanol concentration up to 5% v/v in the gasoline formulation increased the vapor pressure of the mixture. The addition of both ethanol and ETBE in the base gasoline resulted in ternary mixtures which smoothed the behavior of the vapor pressure while they acted as excellent octane improvers.

Biomethane and biogas produced from waste (i.e., from an anaerobic digester) have shown themselves to be promising fuels for internal combustion engines. They can improve fuel security and contribute in reducing emissions, including ${\mathrm{CO}}_2$, when used as a supplement to diesel fuel in dual-fueled diesel engines. In this work the influence of diesel fuel properties, ${\mathrm{H}}_2$ and reformate (${\mathrm{H}}_2$ and CO) additions on the performance of diesel-biogas dual-fueled engines are studied. Biogas, with a composition of 60% ${\mathrm{CH}}_4$ and 40% ${\mathrm{CO}}_2$ by volume, was introduced to the engine intake manifold; reducing the utilization of the in-cylinder injected diesel fuel. Under diesel-biogas fueling, engine out ${\mathrm{NO}}_{\mathrm{X}}$, PM and smoke emissions were reduced. However, the combustion patterns were altered, and under high biogas concentrations (those that were greater than 60% reduction of the diesel fuel) combustion stability became an issue, leading to increased CO and HC emissions. The influence of the in-cylinder injected diesel fuels, on dual-fueled engine operation, were studied by blending low sulfur diesel with 30% by volume synthetic Gas to Liquid (GTL) diesel (named GD30) and pure GTL. Increasing GTL concentration in the diesel fuel blend enhanced combustion stability, fuel economy and improved the emissions of HC, ${\mathrm{NO}}_{\mathrm{X}}$ and PM in diesel-biogas fueled engines. Hydrogen or reformate (${\mathrm{H}}_2$ and CO) addition to a diesel-biogas fueled engine improved engine emissions.

The target of the present work is to review the literature regarding the effects of biodiesel blends on nitrogen oxide (${\mathrm{NO}}_{\mathrm{x}}$) emissions during the transient operation of diesel engines (acceleration, load increase, starting, driving cycles). The most important mechanisms are analyzed on the basis of the fundamental aspects of transient conditions and the effects that biodiesel physical and chemical properties have relative to conventional diesel oil; biodiesel feedstock and driving cycle effects are also emphasized. In parallel, a comprehensive statistical analysis is presented regarding the effects of biodiesel blends on ${\mathrm{NO}}_{\mathrm{x}}$ emissions for engines running on transient cycles during the last 30 years. For the majority of the reviewed transients, an increasing trend in ${\mathrm{NO}}_{\mathrm{x}}$ emissions is established when the biodiesel ratio in the fuel blend increases. Moreover, the biodiesel ${\mathrm{NO}}_{\mathrm{x}}$ emission penalty seems to increase for more aggressive cycles and for increasing feedstock unsaturation.

This study attempts to explore the influence of emulsified palm biodiesel as a pilot fuel in a biogas run dual fuel engine. The intention is to achieve diesel-equivalent performance from a diesel engine, together with a reduction in engine emissions, with complete replacement of fossil diesel with renewable fuels. The results of this study are compared to those for a neat biodiesel (Jatropha)-biogas dual fuel engine run at identical engine settings. For baseline comparison, the results are also compared with a standard diesel run. The results show that with the presence of biogas, emulsified biodiesel as a pilot fuel can present a better dual fuel efficiency (41%) and a lower energy consumption (38%) than neat biodiesel in a piloted study. Also, the presence of a microexplosion of emulsified biodiesel was found to reduce the pilot fuel consumption with the presence of biogas, especially at lower loads, where the burning rate of biogas usually slows down due to the lean gas-air mixture and cooler charge temperature. In addition, emulsified palm biodiesel successfully brings the peak cylinder pressure (PCP) closer (8°ATDC) to top dead center (TDC). This elevates the magnitude of the PCP, which increases the expansion ratio and hence improves engine efficiency. With the presence of emulsified biodiesel, the supply of biogas is found to get reduced, especially at higher loads, which in turn reduces the hydrocarbon emission. However, other emission characteristics are not as exciting, and hence emulsified biodiesel in biogas dual fuel mode needs to be further explored at various engine-operating characteristics in order to obtain a superior emission performance.

Butanol isomer diffusion flames were studied experimentally in a counterflow burner configuration with an emphasis on establishing a difference in extinction strain rate among three fuels with practically identical thermochemistry. An effect of molecular structure on the extinction strain rates of butanol isomers was observed and analyzed in terms of bond dissociation energies. The results indicate that although all isomers share essentially the same adiabatic flame temperature, $n$-butanol flames can sustain a consistently higher extinction strain rate than the flames of other isomers (isobutanol and sec-butanol). Extinction strain rates of isobutanol and sec-butanol were equal, within experimental error. Numerical simulation of $n$-butanol diffusion flames produced results consistent with those measured experimentally and provided insight into the distribution of major species and combustion intermediates. Stable annular flames were observed for all three isomers as a temporary step before extinction.

The application of biodiesel as an alternative to diesel is well recognized. However, having a lesser calorific value than diesel, it results in a lower power and efficiency. This can suitably be improved by emulsifying biodiesel with water. However, the properties of biodiesel emulsions are not similar to that of diesel. Hence, the energy and availability distribution of a biodiesel emulsion–run engine will not be identical to that of a diesel-run engine at standard diesel settings. To enlighten this ambiguous fact of literature, an energy-exergy analysis has been performed for a water-in-biodiesel emulsion run diesel engine for a set of compression ratios (CRs) and injection timings (ITs) at full engine load. The biodiesel considered for the study is palm oil methyl ester (POME). The parameters analyzed are the energy and exergy potential of fuel input, shaft work, cooling water, exhaust gas, and exergy destruction. Side by side, the effects of the variation of CR and IT on peak pressure, peak heat release rate, brake thermal efficiency, exergy efficiency, exhaust gas temperature, and entropy generation rate are also discussed.

Butanol produced from agricultural sources is emerging as a potentially renewable biofuel for use in engine applications. In this work, butanol electrostatic sprays were established within a narrow region of low flow rates. Spray phenomenology was investigated through high-speed visualization for the low flow rate conditions in the vicinity of the lowest voltage for which electrosprays (e-sprays) could be sustained. Spray structure was studied through droplet size and velocity measurements for a combination of conditions, performed by using phase Doppler anemometry. Combined with high-speed spray visualization, these measurements revealed a stable e-spray operation with narrow droplet size and velocity distributions; i.e., spray behavior was close to monodisperse. A similarity analysis was performed to develop an empirical expression correlating appropriately dimensionless average diameter, flow rate, and applied voltage.

This is an experimental and computational study of the effect of a low-percentage biodiesel blend on the operation, diesel filter loading, and fuel additive-assisted regeneration behavior on a conventional, direct injection (DI), single-cylinder diesel engine. The evolution of regeneration was studied by means of infrared thermography on the unit filter. The results of two sets of regeneration experiments, one for each fuel blend, with high-space velocity levels are discussed. The test fuels were conventional diesel (denoted as B0) and B20 biodiesel blend. The objective was to investigate the differences in catalytic soot ignition and regeneration propagation when the engine is fueled by biodiesel blend. The investigation is assisted by the application of an in-house diesel particulate filter (DPF) regeneration modeling tool. The results indicate a faster evolution of the regeneration with B20 fuel, with lower overall filter wall temperatures prevailing, more favorable on filter durability grounds.

Ultraviolet (UV)-visible-near infrared (IR) multiwavelength extinction spectroscopy was applied in the exhaust line of an automotive common rail diesel engine to investigate the postinjection strategy impact on the fuel vapor. Four fuels were tested: a baseline diesel and three blends of diesel with 20% by volume of rapeseed methyl ester (RME), 20% of n-butanol and 20% of RME along with 20% of n-butanol. Experiments were performed at the engine speed of 2,750 rpm and 1.2 MPa of brake mean effective pressure. Preliminary engine tests were carried out to explore the postinjection activation aptitude to produce hydrocarbons at the exhaust, needed for the diesel oxidation catalyst (DOC) and the regeneration of the diesel particulate filter (DPF). Results of hydrocarbon and smoke emissions at the exhaust, with and without postactivation, are presented for the different blends. The optical diagnostic allowed to evaluate, during the postinjection activation, the evolution of the fuel vapor in the engine exhaust line. The spectroscopic investigation was focused on evaluation of the postinjection aptitude and fuel composition to produce hydrocarbon-rich exhaust gaseous. The main results showed that the butanol blended with diesel and/or biodiesel induced a higher concentration of fuel vapor within the exhaust manifold and consequently a lower tendency to lubrication oil dilution.

This paper conducts an extensive experimental campaign for dual fuel biodiesel-producer gas combustion development and the related pollutant emissions and reports the results with the aim of highlighting the effect of biodiesel pilot injection parameters. For this purpose, a common rail diesel research engine was converted to operate in dual fuel mode; the gaseous fuel was introduced into the engine through an indirect injector housed well upstream of the engine intake duct; and the composition of the gaseous fuel simulating the producer gas was obtained using a mixing system able to generate a gaseous mixture of carbon monoxide (CO), hydrogen (${\mathrm{H}}_2$), and nitrogen (${\mathrm{N}}_2$) with the desired amount for each of them. The biodiesel pilot injection required to ignite the gaseous fuel was instead sprayed into the cylinder using a common rail high-pressure injection system. During tests, the biodiesel injection amount, pressure, and advance were varied on several levels, together with the composition and amount of gaseous fuel. The cylinder pressure was sampled and, from it, heat release rate and indicated mean effective pressure were estimated. Moreover, gaseous pollutant emissions at the exhaust were measured. The results demonstrate that biodiesel pilot injection parameters are crucial to control the development of combustion and emission levels when the engine is operated in dual fuel biodiesel-producer gas mode. Therefore, the potentialities of the common-rail high-pressure injection system may be developed to optimize as much as possible the operation of such engines in terms of power output, increase in combustion efficiency, and reduction of environmental impact.

This paper investigates the effect of biodiesel and biodiesel blends on the macroscopic spray behavior, combustion characteristics, and exhaust emissions of a passenger vehicle diesel engine. In this study, the physical properties, macroscopic spray characteristics, and combustion and emissions characteristics of several fuels such as soybean oil biodiesel, canola oil biodiesel, and its blends were examined. Based on the experimental results, the specific gravity of biodiesel and its blends decreased when the temperature increased, and the tendency of specific gravity was similar for the temperature variation of tested fuels. The dynamic viscosity of biodiesel and its blends decreased as the fuel temperature increased. The viscosity differences between the tested fuels also gradually diminished as the fuel temperature increased. The ignition delay of biodiesel fuels was shortened compared to that of conventional diesel fuel, and the ignition delay was reduced by the increase in the biodiesel blended ratio. The combustion pressure of the biodiesel blended fuel had a similar trend, which was slightly higher than that of conventional diesel fuel. The NOx emissions of biodiesel blended fuels increased; however, this rise in NOx emissions was relatively small compared to the increase in NOx resulting from rising fuel injection pressure. The soot emissions were reduced as the biodiesel blending ratio increased.

New-generation biofuels are mainly produced from nonfood crops or waste. Although second-generation ethanol is one of the main options, valeric esters can also be produced from lignocellulose through levulinic acid. However, only few experimental results are available to characterize their combustion behavior. Using a traditional compression ignition (CI) engine converted to monocylinder operation, the engine performances and emissions of butyl and pentyl valerate (BV and PenV, respectively) were investigated. This paper analyses the experimental results for blends of $20{\%}_{\mathrm{vol}}$ of esters in diesel fuel, taking diesel fuel as the reference fuel. The BV and PenV have a smaller cetane number and consequently the ignition delay of the blends is slightly longer. However, engine performances and emissions are not significantly modified by adding $20{\%}_{\mathrm{vol}}$ of esters to diesel fuel. The BV and PenV then represent very good alternative biofuels for CI engines.

One of the approaches to improving the fuel properties of biodiesel, a fuel derived from vegetable oils, animal fats, or other triacylglycerol-containing materials, is to use a feedstock with inherently different fatty acid profile than most common feedstocks such as commodity vegetable oils. Cuphea oil is such a feedstock as it is highly enriched in decanoic acid, which causes the biodiesel fuel derived from it to exhibit improved properties. Cuphea oil, however, faces agronomic issues before widespread commercial production is possible. This article briefly summarizes recent research results regarding cuphea oil in relation to the biodiesel fuel derived from it.