Journal of Energy Engineering

This paper deals with the effects of adding Jet A-1 fuel to ethanol (E) in proportions of 20/80 vol% in biofuel homogeneous charge compression ignition (HCCI) combustion. Experiments were performed with a four-stroke direct injection (DI) diesel engine, the first cylinder of which was converted to operate in HCCI mode with various air/ethanol and air/Jet20E80 mixtures characterized by relative air:fuel ratios of $\lambda =3.01-2.02$ and 3.84−1.90 and externally prepared in the intake manifold at the inlet air temperature of 100°C. We studied the effects of Jet20E80 fuel blends on start of combustion (SOC), maximum heat release rate, burn angle mass burn fraction (MBF) 50, combustion duration, maximum in-cylinder pressure, and temperature indicated mean effective pressure (IMEP), thermal efficiency, coefficient of variation (COV) of maximum in-cylinder pressure and IMEP, as well as smoke and exhaust emissions. The air/Jet20E80 mixture improved HCCI combustion-phasing control, suggesting higher engine efficiency and ecological benefits. The start of combustion (SOC) occurred 2.2 crank angle degrees (CAD) later in the cycle, which enhanced the maximum heat release rate and the peak in-cylinder pressure by 37.2 and 23.1% and IMEP and thermal efficiency by 49.0 and 16.0%, respectively. The IMEP coefficient of variation decreased to its lowest level, 3.73%, when running with the richest air/Jet20E80 mixture, $\lambda =1.90$, at a constant speed of 1,400 rpm. The production of $\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$ and total unburned hydrocarbon (THC) emissions decreased 2.8 and 1.3 times, while smoke and CO emissions were 2.5 and 1.6 times higher than the amounts that HCCI combustion of neat ethanol produces under these conditions.

This paper focuses on a four-cylinder light-duty diesel engine and analyzes how the coupling action of oxygenated fuel and gas circuit oxygen impact soot generation based on tests where the in-cylinder ambient oxygen concentration is rich, medium, or poor. The test results show that ignition delay period and fuel oxygen content are major factors in soot value decreases, whereas in-cylinder combustion temperature hardly affects soot generation. Further analysis reveals that the weight of influence of ignition delay period and fuel oxygen content on soot generated by combustion of B0 (pure diesel) and B20 (20% n-butyl alcohol + 80% diesel by mass) fuels are different at various in-cylinder oxygen concentrations. For an oxygen content of 0.87% in the fuel, when there is rich oxygen inside the cylinders, the weight of influence on soot generation is 72.73–80.00%; when there is a medium amount of oxygen, the weight of influence is 42.18–72.73%; in the case of scarce oxygen, the weight of influence is 41.43–42.18%. In terms of ignition delay period, when there is rich oxygen, the weight of influence is 20.00–27.27%; in the case of a medium amount of oxygen, the weight of influence is 27.27–57.82%; and for only a little oxygen, the weight of influence is 57.82–58.57%.

Controlled autoignition delay is considered a very promising new technology, having the potential of combining low fuel consumption with low pollutant emissions. In this study, the effect of pure diesel fuel and biodiesel B20 (20% rapeseed oil mixed with 80% diesel fuel, by volume) on ignition delay period, at different engine speeds, under full load operating conditions, has been investigated experimentally and numerically. For this purpose, two models were proposed. The experimental results were compared with the ignition delay predicted by some correlations and by the considered models. The results showed that the ignition delay period of biodiesel B20 is shorter than that of pure diesel fuel at similar operating conditions. Regarding pure diesel fuel, the ignition delay periods are in good accordance with Arrhenius type correlations, whereas for biodiesel B20 the correlation results are significantly different than the experimental data.

Combustion behaviors and carbon monoxide emission characteristics of four kinds of coals and their blends, which were shaped into pellets, were investigated in a drop-tube furnace with various gas flow temperature (650–850°C) and oxygen concentration (10–70%). Pellets of 6 mm were hung by a wire basket and the combustion process was recorded at 60 frames/s using a high-performance camera. The ignition of the bituminous pellet was found to be homogeneous but it was heterogeneous for anthracite. When the oxygen concentration was more than 50%, an obvious fragment was found for the anthracite pellet, which caused higher surface temperature compared with the predicted temperature. The instantaneous CO emission of the bituminous coal had two peaks, whereas there was only one peak for that of anthracite. The total CO emission decreased exponentially when the temperature and oxygen concentration increased, and the oxygen concentration had more influence on the reduction of CO emission. CO generation was also affected by coal type; the higher the carbon and ash component of the coal, the more CO was generated with the same conditions.

The combustion process in a single-cylinder turbocharged diesel engine with a pilot-pilot-main injection strategy was simulated using a computational fluid dynamics software. The effect of injection timing on the combustion process as well as the generation of NO and soot was analyzed in detail. It was revealed that the retardation of injection timing causes the pressure in the cylinder to decrease gradually. The main heat release peak also reduces while the premixed combustion fraction increases, and this causes the position of the heat release peak to move away from top dead center. At the moment of 10% heat release ($q_{10}$) with retarding the injection timing, soot generation decreases as the lean premixed combustion takes the major position while more NO is generated due to rapid heat release of the premixed mixtures. At the moment of 90% heat release ($q_{90}$), NO emission is decreased due to the low temperature in the cylinder. Soot generation is increased initially and later decreased due to the extended combustion space and higher premixed combustion fraction. Therefore, a favorable trade-off between ${\mathrm{NO}}_x$ and PM emissions is well compromised in a diesel engine adopting a low-temperature premixed charge compression ignition (PCCI) mode.

Ethanol and n-butanol are promising oxygenates to be used in blends with fossil diesel fuel because they have the potential to significantly decrease the particulate matter emissions of compression ignition engines. Moreover, they can be produced from renewable sources, which can help reduce dependence on fossil fuels. In this work, ethanol and n-butanol were each used in four blends with a standard ultra-low-sulfur diesel. The eight samples created are characterized by the same oxygen content per pair, obtained either by use of ethanol or n-butanol, respectively. The effects of each alcohol in terms of mixture stability, ignition quality, and other physicochemical properties were investigated. Finally, the effects of the eight samples on the performance and exhaust emissions of a typical stationary diesel engine operating at steady-state conditions were studied. The results showed that both alcohols contribute to the reduction of particulate matter emissions while causing minor changes to most physicochemical properties.

This study focuses on the introduction of a new biodiesel resource, Kachnar seed oil (KSO). The raw oil was extracted from the seed by Soxhlet extraction. The composition of fatty acids and physicochemical properties of the raw oil were measured. Methyl ester was produced from the raw Kachnar seed oil using a transesterification process using an alkaline catalyst. The new biodiesel, Kachnar methyl ester (KME), meets biodiesel standards and could be a reliable substitute for diesel in diesel engine applications. This paper also investigates a methodology to improve the oxidation stability of Kachnar biodiesel by blending it with diesel and by using different commercially available antioxidants, namely butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA), propyl gallate (PG), and pyrogallol (PY), in the produced biodiesel. The antioxidants were dosed in concentrations ranging from 100 to 1,000 parts per million (ppm). The result of the investigation shows that antioxidants PY and PG demonstrated effective results for improving oxidation stability of Kachnar biodiesel. TBHQ was the least effective among the investigated antioxidants, whereas the KME10 blend can maintain its stability without any antioxidant.

Using natural gas as a supplement for the conventional diesel fuel in a compression-ignition environment—a natural gas/diesel dual-fuel (NG/DDF) engine—seems to be a solution for reducing soot and nitric oxide (NO) emissions in existing and future diesel motor vehicles. NG/DDF operation, compared with that of conventional diesel engines, suffers from higher specific energy consumption (SEC) and higher carbon monoxide (CO) and unburned hydrocarbons (HC) emissions. This seems to become more apparent at part-load operations. Diesel injection pressure (DIP) and cylinder pressure (CP) of the charge at the inlet valve closing (IVC) event ($P_{\mathrm{IVC}}$) are two critical engine parameters which affect performance characteristics and pollutants of NO, CO, and soot of a NG/DDF engine. This work studies theoretically the effects of DIP and $P_{\mathrm{IVC}}$ on the performance and exhaust emissions (NO, CO, and soot) of a light-duty diesel engine operated with methane, which is the chief component of natural gas. The study is carried out using a custom-built model, which is two-zone and of the phenomenological type. The accuracy of the modeling results is tested by using corresponding experimental data acquired by an extensive experimental study performed previously on a NG/DDF engine. The primary objectives of this comparative appraisal are to specify the effects of the aforementioned parameters on the emitted pollutants and the performance characteristics of the specific engine, and to record the disadvantages and advantages. The conclusions of the specific investigation are useful, particularly to identify the optimum combination of the strategies for improving the overall performance of an existing compression-ignition (CI) engine operating with natural gas/diesel.

In this paper, operating characteristics of an on-board proton exchange membrane electrolysis (PEMe) hydrogen generator integrated with a spark ignition (SI) engine were investigated. The effect of ${\mathrm{H}}_2$ and ${\mathrm{O}}_2$ produced by the PEMe, which is fed by the engine charging system on the in-cylinder combustion and engine performance parameters, was investigated experimentally for different engine operating conditions. Also, the PEMe inlet water was heated by a copper pipe passing through a heat exchanger positioned on the engine exhaust path to decrease the PEMe power requirement. Therefore, improving the engine performance parameters by decreasing the engine charger system activity was attempted. The SI engine was operated along with integrated on-board PEMe for different engine speeds, throttle positions (TP), and engine loads. As a result, an on-board PEMe hydrogen generator system integrated with a SI engine caused improvement of the performance parameters (i.e., brake power, brake torque, brake thermal efficiency, and brake specific fuel consumption) in the range of 3.16–4.04% when the engine was operated with $1/2\mathrm{TP}$ and a range of 1,600–3,600 rpm. However, the low and medium speeds of the engine are more advantageous than high engine speeds with regard to the on-board PEMe system efficiency.

The present work investigates the effect of the injection dwell time and injection pressure on soot reduction potential in an optical single-cylinder light-duty diesel engine. The engine operated under a double-injection scheme under low load and low engine speed conditions. The conducted experiments considered two different dwell times for three different injection pressures. The fuel quantity of the main injection was adjusted to maintain the same indicated mean effective pressure (IMEP) value among all cases considered. Findings were analyzed via means of pressure trace and apparent heat release rate (AHRR) analyses, as well as a series of optical diagnostics techniques, namely high-speed imaging and planar laser-induced incandescence (pLII). The combination of dwell time and injection pressure substantially affects charge reactivity and soot oxidation potential. The analysis suggests that a shorter dwell time combined with a higher injection pressure can lead to an enhanced potential for engine-out particulate reduction by creating an in-cylinder environment that promotes soot oxidation. Overall, results indicate that a close-coupled pilot and main injection scheme can reduce soot levels, albeit while increasing specific fuel consumption by up to 12% to maintain the same engine power output levels.

A miniature supersonic burner has been designed with the purpose of studying extreme flow-chemistry interaction. The system combines a first-stage, a lean premixed methane/air burner that creates a vitiated flow at elevated pressure, and a second stage where additional fuel (methane) is added into the flow before exiting the system through a converging nozzle. At the system exit, a sonic underexpanded jet is created where very short characteristic fluid time scales obtain. These are comparable to the fastest chemical reaction time scales, thus creating a situation where the flow interacts with the chemistry and suppresses combustion. In this paper, reduced-chemistry three-dimensional computational fluid dynamics is used to understand the reacting flow in the system and predict flame holding, while vibrational Raman line-imaging spectroscopy is used—qualitatively—at the burner exit. Experiments and computations point to a clear bimodal behavior of the system: in one extreme, where an attached non-premixed flame is created in the burner; in the other extreme, where no reaction is taking place in the second stage and all additional fuel is left unburnt.

A miniature supersonic burner has been designed with the purpose of studying extreme flow-chemistry interaction. The system combines a first-stage, lean premixed methane/air burner that creates a vitiated flow at pressure and a second-stage burner where additional fuel (methane) is added to the flow before exiting the system through a converging nozzle. In this part, a one-dimensional (1D) detailed chemistry calculation of the reacting flow at the exit of the jet is conducted. The mixture of gases is allowed to expand isentropically to the conditions expected at the exit of the supersonic jet. The viscous and conducting flow field through a shock wave is calculated using the GRI3.0 kinetic scheme. The structure of the standing detonation downstream of the Mach stem is examined for different initial concentrations of hydrogen atoms. Results point to the extreme suppression of chemistry through the supersonic flow field and the creation of low Damköhler numbers in the exit of the miniature burner.

The paper presents a new integrated model for calculating the thermophysical properties of marine heavy fuel oil (HFO). The model considers HFO as an equivalent one-component heavy petroleum fraction with undefined composition and requires as input four values of fuel bulk properties commonly measured at fuel bunkering. Thus, the model accounts for any HFO quality stored onboard a vessel. The model predicts a large set of fuel properties relevant for engine computational fluid dynamics (CFD) studies, including temperature dependence. First, model validation is performed by means of measurements of a number of properties for different HFO qualities. Next, the model is applied to calculate the thermophysical properties of seven widely used marine heavy fuel grades as prescribed by current standards. Finally, the model is tested with CFD simulations of nonreactive HFO spray flow in a large constant-volume chamber, and the results are compared against recent experiments. Computational results are in very good agreement with experiments. Overall, the present model is deemed very promising, yielding a solid basis for CFD studies of HFO combustion in marine engines.

The combination of heat transport and heat-work conversion processes in thermal systems highlights the importance of the integrated modeling and optimization method. Following the analogy between power flow and heat transfer, this study introduces a power flow model for a building heat transport and gas refrigeration system that combines the linear temperature difference-based thermal resistances, energy sources, and additive thermo-motive forces. Holistic system constraints are deduced from the power flow model and constructed by combining Kirchhoff’s law with the heat-work conversion equations. The constraints represent each component’s performance and the system topological characteristics and reveal the system-level overall thermal energy transport and conversion discipline. For validation, an optimization case that minimizes the net input work of this system is introduced. The results show that the same heat capacity rates are necessary for the ambient and indoor air for the minimum net input work. Meanwhile, improvements in building thermal insulation performance and incremental increases in the total thermal conductance of the heat exchangers and total heat capacity rates of the working fluid all reduce the net input work. That is, the power flow method is a feasible and useful tool for the integrated modeling and optimization of thermal systems such as thermal management in the building or aircraft fields.

The purpose of this work was to investigate the effect of the combustion and emission characteristics of dimethyl ether (DME), diesel fuel, and a DME-biodiesel blend on a passenger vehicle diesel engine. In this study, DME properties, atomization characteristics, and effects of the exhaust gas recirculation (EGR) rate on the combustion performance and emission characteristics of a diesel engine were investigated under single and split injection. The results show that DME atomization is better than that of conventional diesel fuel, and that increasing the EGR rate decreases the combustion pressure and heat release rate of the DME-biodiesel blend. Upon comparison, the maximum pressures of the pilot injections were significantly lower than those of the single injection for the DME-biodiesel. In addition, the maximum pressure decreased with the increasing EGR rate. However, the decrease was small compared with that of the pilot injection strategy. Exhaust emissions from the engine showed that increasing the EGR rate decreased combustion pressure and nitrogen oxide emissions, and increased hydrocarbon and carbon monoxide emissions. The soot was almost zero for the DME-biodiesel fuel and for the EGR rate variations.