Search Results

The present paper aims to discuss the quality characteristics of Jet Fuels used in the Greek market in comparison with fuels used in other countries and to evaluate jet fuels along with diesel and biodiesel on a diesel engine. To establish the quality characteristics for Jet Fuels of the Greek market, fuel samples were collected from the local refineries on a regular basis, thus monitoring the fuel quality fluctuation over time. JP8, along with diesel and biodiesel, were used alone and in mixtures on a single cylinder stationary diesel engine. Emissions and volumetric fuel consumption were measured under various loads.

To reduce the fuel related logistic burden, NATO Armed Forces are advancing the use of a single fuel for both aircraft and ground equipment. To this end, F-34 is replacing distillate diesel fuel in many applications. Yet, unacceptable wear due to poor lubricity was illustrated by tests conducted with kerosene on High Frequency Reciprocating Rig. Therefore, HFRR tests were performed with fatty acid methyl esters of sunflower, palm, cotton-seed, tobacco-seed, olive, rape-seed and used frying oils, at volume concentrations from 0.05% to 0.6%. This study showed that the biodiesels used, produced a significant decrease in the wear scar diameter at concentrations of 0.2% to 0.4 %. Biodiesels derived from non-polyunsaturated oils, such as palm and olive gave better lubrication at certain concentrations.

In this work, a quasi-dimensional, multi-zone combustion model is analytically presented, for the prediction of performance and nitric oxide (NO) emissions of a homogeneous charge spark ignition (SI) engine, fueled with biogas-H2 blends of variable composition. The combustion model is incorporated into a closed cycle simulation code, which is also fully described. Combustion is modeled on the basis of turbulent entrainment theory and flame stretch concepts. In this context, the entrainment speed, by which unburned gas enters the flame region, is simulated by the turbulent burning velocity of a flamelet model. A flame stretch submodel is also included, in order to assess the flame response on the combined effects of curvature, turbulent strain and nonunity Lewis number mixture. As far as the burned gas is concerned, this is treated using a multi-zone thermodynamic formulation, to account for the spatial distribution of temperature and NO concentration inside the burned volume.

The objective of this work was the assessment of aliphatic amines and tertiary dialkyl-amides as lubrication additives or extenders, on ultra - low sulfur diesel fuels. In order to evaluate the influence of two types of nitrogen compounds on the lubrication properties of ultra - low sulfur diesel fuels, nine distillation fractions produced by atmospheric distillation of a hydrotreated diesel fuel, were used as the base fuels. Five aliphatic amines and two tertiary amides were used as lubricating additives at five different concentrations i.e. 0.5, 1.0, 2.0, 4.0 and 6.0% by volume, on the nine base fuels. Tribological experiments were carried out on the High frequency Reciprocating test Rig (HFRR). The wear results showed that only four of the five aliphatic amines used, provide satisfactory HFRR mean wear scar diameter (WS 1.4) of less than 460 microns, and at the concentration levels of 1-2% by volume. The concentration levels below 1 % by volume had no effect on the fuel lubricity.

Pollutant emissions and specifically NO and soot are one of the most important problems that engineers have to face when developing heavy duty DI diesel engines. Two main strategies exist as options for their control, reduction inside the engine cylinder using advanced combustion and fuel injection technologies and use of after-treatment systems. In the present work it is examined the use of EGR to control the formation of NO inside the cylinder of an engine with extremely high peak pressure. The work is applied on a single cylinder truck test engine developed under a project funded by the European Community focusing on the improvement of heavy duty DI diesel engine efficiency using increased injection timing. Use is made of a simulation model to predict the effect of more advanced injection timing on engine performance and emissions. The model has been modified to include the effect of EGR used to c ontrol the formation of NO which is considerably increased at high injection timings.

This study examines the effects of neat soy-based biodiesel (B100) and its 50% v/v blend (B50) with low sulphur automotive diesel on vehicle PAH emissions. The measurements were conducted on a chassis dynamometer with constant volume sampling (CVS) according to the European regulated technique. The vehicle was a Euro 2 compliant diesel passenger car, equipped with a 1.9 litre common-rail turbocharged direct injection engine and an oxidation catalyst. Emissions of PAHs, nitro-PAHs and oxy-PAHs were measured over the urban phase (UDC) and the extra-urban phase (EUDC) of the type approval cycle (NEDC). In addition, for evaluating realistic driving performance the non-legislated Artemis driving cycles (Urban, Road and Motorway) were used. Overall, 12 PAHs, 4 nitro-PAHs, and 6 oxy-PAHs were determined. The results indicated that PAH emissions exhibited a reduction with biodiesel during all driving modes.

Biofuels are a promising alternative to fossil fuels as their availability has been reduced during the last decades and they are the main sources of greenhouse gases emissions. Moreover, the targets of the international regulations include reduction of fossil fuels consumption, and improvement of the sustainability of the vehicle fleet. Blending gasoline with biofuels will result in changes in fuel blending procedures and combustion process especially for the gasoline direct injection (GDI) engines. In this article, flame visualization using chemiluminescence techniques in a Single Cylinder Optical Research Engine (SCORE) is presented, with an adjusted intake pressure of 850 mbar and early intake single injection (280 CAD BTDC), by using 100% hydrocarbon-based gasoline, E10 (90% gasoline - 10% ethanol) and ETBE20 (80% gasoline - 20% ethyl tert-butyl ether). ETBE20 is a potential alternative for E10, as it contains the same amount of renewable fuel and has low water solubility.

Simulation models are widely used from research engineers to investigate the combustion mechanism of DI diesel engines. These models can be used, as tools to either comprehend information provided by experimental data or to perform predictions and assist the development process. As widely recognized a valuable source of information for engine performance and emissions studies is the cylinder pressure trace. It can provide after processing information concerning the combustion rate of fuel injected inside the combustion chamber. Often it is also used to calibrate simulation models or even to derive correlations to represent the combustion rate of fuel inside the combustion chamber. The present research team has during the development process of a simulation model for the description of DI diesel engine performance and emissions realized that there exists a serious problem.

During the last years a great effort has been made by many NATO nations to move towards the use of one military fuel for all the land-based military aircraft, vehicles and equipment employed on the military arena. This idea is known to as the Single Fuel Concept (SFC). The fuel selected for the idea of SFC is the JP-8 (F-34) military aviation fuel which is based upon the civil jet fuel F-35 (Jet A-1) with the inclusion of military additives possessing anti-icing and lubricating properties. An extended experimental investigation has been conducted in the laboratory of Thermodynamic and Propulsion Systems at the Hellenic Air Force Academy. This investigation was conducted with the collaboration of the respective laboratories of National Technical University of Athens and Hellenic Naval Academy as well.

In the present work a sensitivity analysis is conducted using a multi-zone phenomenological model developed in the past by the author's, to estimate the effect of model's constants on engine performance and emissions. The constants used for this analysis are those embedded in the semi-empirical relations of the model, regarding air entrainment rate, combustion rate, ignition delay and evaporation rate. The model is applied on a heavy duty supercharged DI diesel engine and the effect of each of these constants on measurable engine parameters is defined. From the sensitivity analysis the relation between model constants and engine output data is derived. These results are used to define a constants determination procedure. The target is to define a limited number of adjustable constants so that the procedure can be of practical use. Following this, the calibration procedure is applied to determine the value of each constant, at various engine speeds and loads for the engine in question.

A second-law analysis is performed in both chambers of an indirect injection turbocharged diesel engine and the simulation program developed is used to study the second-law performance of the engine at various operating conditions, steady state and transient. The simulation developed is based on the filling and emptying approach and provides detailed analysis of thermodynamic, dynamic and second-law differential equations on a degree crank angle basis. It incorporates a detailed mathematical simulation of the fuel pump and solves each equation separately for each one of the six cylinders of the engine in hand. The model is validated against experimental data at steady state and transient conditions, obtained at the authors' laboratory. The prechamber rate and cumulative availability terms and irreversibilities are computed and depicted against the main chamber ones during the 720 degrees crank angle of an engine cycle.

In this study, regulated, unregulated exhaust emissions and fuel consumption with ultra low sulphur diesel and soy-based biodiesel blends at proportions of 10 and 30% v/v have been investigated. A Euro 4 compliant SUV, equipped with a 2.2 litre common-rail diesel engine and an oxidation catalyst was tested on a chassis dynamometer with constant volume sampling (CVS) technique. Emission and fuel consumption measurements were performed over the New European Driving Cycle (NEDC) and the non-legislated Artemis driving cycles which simulate urban, rural, and highway driving conditions in Europe. The regulated pollutants were characterized by determined NOx, PM, CO, and HC. CO2 was also quantified in the exhaust. Overall, 16 PAHs, 4 nitro-PAHs, 6 oxy-PAHs, 13 carbonyl compounds and particulate alkanes ranged from C13 to C35 were determined in the exhaust.

The ability of a catalyst to enhance the performance of synthesized biobased lubricant basestock was investigated in this study. Pomace olive oil, cottonseed oil, used frying oil and methyl oleate were utilized as starting materials for the production of the biobased lubricants and a two stages transesterification methodology was followed. Initially the oils were converted to their corresponding fatty acid methyl esters via methanolysis. The resulting methylesters were subsequently transesterified with TMP producing the desired oleochemical ester. These syntheses were carried out in the presence of either sodium methoxide or Ca/TEA alkoxide as catalysts. Following the purification phase, the synthesized esters were evaluated as potential biolubricants regarding their physicochemical properties such as viscosity index, pour point and acid value.

Many incidents associated with filter plugging have extensively been reported in microbially contaminated diesel and biodiesel fuel systems, especially under long term storage conditions. In this study a quantitative assessment of the undesirable insoluble solids produced in contaminated biodiesel fuels was carried out in order to evaluate their evolution rate during biodeterioration. For this purpose, a series of contaminated biodiesel fuel microcosms were prepared and stored for six months under stable conditions. The quantity of the particulate contaminants was monitored during storage by a multiple filtration technique which was followed at the end by a comparison with the active bioburden per ATP bioluminescence protocol. Additionally, identical microcosms were treated with a commercially available biocide in order to examine the latter’s activity both on solids formation and the microbial proliferation.

The current work uses a method developed by the authors for both combustion irreversibility and working medium availability computations in a high speed, naturally aspirated, four stroke, internal combustion engine cylinder. The objective of the study was to extrapolate already published results of the second-law analysis of diesel engine operation by studying parametrically the effect of main operating parameters such as engine speed of rotation, injection timing, and fuel composition. Extensive experimental data were available for the case of dodecane injection, which were used for the determination of the fuel reaction rate. Computationally, the same reaction rates were used for methane and methanol injection. The production rate of irreversibility during combustion was analytically calculated as a function of the fuel reaction rate with the combined use of first and second-law arguments and a chemical equilibrium hypothesis.

One of the concerns for biolubricants is the improvement of their oxidation resistance. In this paper the oxidative behavior of seven different types of biobased lubricants basestocks is examined. The aim was to study their relative oxidation stability and also to investigate their response to various antioxidants. The renewable lubricants were treated with four antioxidant additives at a concentration of 0.5% wt. and a comparative assessments of the latters' effectiveness in suppressing the oxidation rate was carried out. Alterations in the acid value were examined as well as relative changes of the oxidized samples by FTIR spectroscopy. The oxidation stability was assessed by employing a Rapid Small Scale Oxidation Test (RSSOT) apparatus according to the accelerated oxidation stability standard method ASTM D7545/EN16091. RSSOT is a relatively new method and thus the behaviour of biobased lubricants and antioxidant agents in this accelerated method has not been thoroughly examined.

Problems with the low-temperature operability performance of biodiesel in blends with petroleum diesel are infrequent, but continue to limit the use of biodiesel during winter months. A troubling aspect of this problem is that in some cases precipitates above the blend Cloud Point (CP) have been detected and have led to plugging of fuel filters and subsequent engine stalling, as well as plugging of fuel dispenser filters. Many researchers found that the saturated monoglyceride content was a main component of the material that was found on plugged fuel filters, as well as traces of Saturated DiGlycerides (SDG), were also present on the plugged fuel filters. This is the reason which forced the organization of standardization to suggest a procedure in order to predict the content of the Saturated MonoGlycerides (SMG) even with uncertainty which can vary from −50% to +50%. The model which was used will be the same as that which was introduced in the Annex C of EN 14214+A1:2013.

The aim of this study is to investigate the lubricity of hydrocarbons that constitute components of petroleum diesel fuel. A number of typical hydrocarbon compounds were selected as representative of the group types of alkanes (paraffins), cycloalkanes (naphthenes) and aromatics, similar to those that are present in diesel fuel. The lubricity of these substances was examined in a High Frequency Reciprocating Rig (HFRR) apparatus according to the ISO 12156-1 standard method. Thereafter, a series of diesel surrogate fuel were prepared from the above substances based on literature data for diesel fuel composition and on the previously obtained results. These model fuels were assessed regarding their lubricating performance in order to evaluate how each individual component can affect the lubricity of the final fuel.

This study examines the impact of ETBE and ethanol addition on the main properties of motor gasoline. European Union mandates the use of biofuels in all transport fuels, according to the 2003/30/EC Directive. The addition of ethanol, a known octane enhancing component, in small proportions significantly increases the vapor pressure of the final gasoline, exceeding the maximum specification limits. ETBE (ethyl tert-butyl ether) is on the other hand an excellent but expensive octane enhancing component with beneficial impact on vapor pressure of the final gasoline. This paper examines the ability of ETBE to act as a stabilizer in gasoline - ethanol blends. Two gasoline samples with different chemical compositions and characteristics were prepared by blending basic refinery components. In each sample, ETBE was added in concentrations of 2, 4, and 6 % V/V respectively. In each of these ETBE - gasoline blends, ethanol was added in concentrations from 1 to 6 % V/V in 1% steps.

The system identification procedure is a powerful and flexible tool for the modeling of dynamic systems. This paper implements the theory of parametric identification in order to estimate a valid model of a flexible robotic arm. For this purpose experimental data is used for the estimation of ARMAX SISO models. A two-stages identification procedure (non-parametric & parametric) provides an insight about the system under identification. In the first stage, known signal analysis methods are applied (correlation-spectral analysis) for the estimation of frequencies and frequency response, and in the second stage, the estimation of ARMAX models is performed in order to fit a transfer function model to collected input-output data set. For the estimation of model's coefficients, use of Evolutionary Algorithms is implemented.