Bernardo Tormos

New methodology for in-cylinder pressure analysis in direct injection diesel engines: application to combustion noise

The objective of this paper is to present a new methodology for the analysis of in-cylinder pressure in direct injection (DI) diesel engines. Indeed, for some applications, the traditional study of total pressure is shown to be insufficient and the proposed technique is intended to be an alternative and more efficient tool, since it may provide a better understanding of the physical mechanisms. The main idea is to decompose the in-cylinder pressure evolution according to three phenomena taking place during diesel engine operation: pseudo-motored, combustion and resonance excitation. In order to validate this new method, it is applied to combustion noise analysis. Actually, the combustion process in DI diesel engines may be considered as an important source of noise, and the traditional approach is mainly based on the interpretation of objective overall spectral levels of both in-cylinder pressure and radiated noise, obtained from Fourier analysis. However, this approach has been shown unable to describe all the relevant aspects of the problem, whereas the results obtained from the proposed decomposition technique exhibit a fair qualitative correlation between in-cylinder pressure and combustion noise issues. Further development of this approach could provide a useful tool for the development of optimal injection strategies fulfilling not only performance considerations but also sound quality requirements for combustion noise in DI diesel engines.

Analytical approach to wear rate determination for internal combustion engine condition monitoring based on oil analysis

Abstract Wear has important, negative effects on the functioning of engine parts. Additionally, this situation is very difficult to evaluate accurately in oil analysis for engine condition monitoring. Original Equipment Manufacturers (OEM), lubricant suppliers and oil analysis laboratories provide specific guidelines for wear metal concentrations. These limits provide good general guidelines for interpreting oil analysis data, but do not take into account common factors that influence the concentration of wear debris and contaminants in an oil sample. These factors involve oil consumption, fresh oil additions, etc., and particular features such as engine age, type of service, environmental conditions, etc. In this paper, an analytical approach to enable a more accurate wear determination from engine oil samples is developed. The above factors are taken into account and an improved maintenance program for internal combustion engines based on oil analysis is developed.

Detection and Diagnosis of Incipient Faults in Heavy-Duty Diesel Engines

This paper proposes a new methodology for detecting and diagnosing faults found in heavy-duty diesel engines based upon spectrometric analysis of lubrication samples and is compared against a conventional method, the redline limits, which is utilized in a number of major laboratories in the U.K. and across Europe. The proposed method applies computational power to a well-known maintenance technique and consists of an improved method of preprocessing to form a derivative tuple, which extracts further information from the measured elemental concentrations. To identify incipient faults, the distance in vector space is calculated using a Gaussian contour, generated from prior data, as the zero crossing, which enables novel samples to be classified as normal or abnormal. This information is utilized as the input to a probabilistic directed acyclic graph in the form of a belief network. This network provides a prognosis for the mechanism as well as suggesting possible actions that could be taken to rectify the diagnosed problem, supported with confidence probabilities. The proposed method is evaluated for both accuracy in detecting a fault as well as the duration of time that is provided before the event occurs, with significant improvements in both metrics demonstrated over the conventional method.

The potential of Large Eddy Simulation (LES) code for the modeling of flow in diesel injectors

This work deals with numerical simulations of the internal flow in diesel injectors, evaluating the skills of the Large Eddy Simulation (LES) code for capturing the turbulent patterns present in the flow. In order to evaluate the potential of the LES code, the results of the simulations have been compared to standard numerical RANS method results, and simultaneously validated with experimental values and DNS data. The experiments were made using special diesel injector geometry, reaching a high injection pressure condition and so ensuring a turbulent regime. In general, results show good agreement with the experimental values and DNS data. It was found that LES is capable of reproducing the turbulent structures in diesel nozzles, and as expected is more accurate than RANS, mainly in the boundary layer.

Proposal of an FTIR Methodology to Monitor Oxidation Level in Used Engine Oils: Effects of Thermal Degradation and Fuel Dilution

This article describes a procedure, based on ASTM standards D7214 and E2412, that has been defined to improve quantification of oil oxidation in used engine oils. Taking into account typical problems that can be found in this type of sample, including thermal oxidation and fuel dilution, Fourier transform infrared (FTIR) spectra were analyzed also considering the effect of the oil formulation. Two zones were considered inside the typical wavenumber range for quantification of oxidation, where those problems can be detected and assessed more easily: zone A between 1725 and 1650 cm−1, where the main oxidation products, such as aldehydes, carboxylic acids, and ketones, occur due to thermal degradation of the oil; and zone B between 1770 and 1725 cm−1, where esters due to potential biodiesel dilution problems are detected.

Using one-dimensional modelling codes to analyse the influence of diesel nozzle geometry on injection rate characteristics

A combined experimental and computational investigation was performed in order to evaluate the influence of nozzle geometry on fuel injection rate and the injector dynamic of a Common-Rail fuel injection system for DI Diesel engines. The method for modelling the most critical parts of the injector have been explained in previous publications and the results confirm that the model is capable of predicting injector hydrodynamic behaviour. A series of parametric studies were performed to evaluate the influence of the nozzle seat type (VCO and microSAC) and the nozzle orifice geometry (cylindrical and conical). Experimental results of the fuel injection rate were included to validate the models. Furthermore, two commercial one-dimensional modelling codes have been used to carry out the study, obtaining excellent results using both codes.

Impact of Spark Assistance and Multiple Injections on Gasoline PPC Light Load

Along the last years, engine researchers are more and more focusing their efforts on the advanced low temperature combustion (LTC) concepts with the aim of achieving the stringent limits of the current emission legislations. In this regard, several studies based on highly premixed combustion concepts such as HCCI has been confirmed as a promising way to decrease drastically the most relevant CI diesel engineout emissions, NOx and soot. However, the major HCCI drawbacks are the narrow load range, bounded by either misfiring (low load, low speed) or hardware limitations (higher load, higher speeds) and the combustion control (cycle-tocylce control and combustion phasing). Although several techniques have been widely investigated in order to overcome these drawbacks, the high chemical reactivity of the diesel fuel remains as the main limitation for the combustion control. The attempts of the researchers to overcome these disadvantages are shifting to the use of fuels with different reactivity. In this sense, gasoline PPC has been able to reduce emissions and improve efficiency simultaneously, but some drawbacks regarding controllability and stability at low load operating conditions still need solution. In this field, previous researches have been demonstrate the multiple injection strategy as an appropriate technique to enhance the combustion stability. However, PPC combustion has been found limited to engine loads higher than 5 bar BMEP when using fuels with octane number greater than 90. In this regard, previous work from the authors showed the capability of the spark plug to provide combustion control in engine loads below this limit even using 98 ON gasoline. The main objective of the present work is to couple the control capability of the spark assistance together with an appropriate mixture distribution by using double injection strategies with the aim of evaluating performance and engine-out emissions at low load PPC range using a high octane number gasoline. For this purpose the optical and metal version of a compression ignition single-cylinder engine, to allow high compression ratio, has been used during the research. A common rail injection system enabling high injection pressures has been utilized to supply the 98 octane number gasoline. An analysis of the incylinder pressure signal derived parameters, hydroxyl radical (OH*) and natural luminosity images acquired from the transparent engine as well as a detailed analysis of the air/fuel mixing process by means of a 1-D in-house developed spray model (DICOM) has been conducted. Results from both analysis methods, suggest the spark assistance as a proper technique to improve the spatial and temporal control over the low load gasoline PPC combustion process. A noticeable increase in the cycle to cycle repeatability (5% versus 15.1% CoV IMEP at 2 bar load) as well as a reduction in the knocking level (20.5 versus 33.6 MW/m at 7 bar load) is observed. In addition, the combination of the spark assistance with the use of the double injection strategy provides a great improvement in terms of combustion efficiency (93% versus 88% for a single injection strategy) with a benefit around 18% in the IMEP.

Large Eddy Simulation for high pressure flows: Model extension for compressible liquids

The present study gives a general outline for the fluid-dynamical calculation of flows at high pressure conditions. The main idea is to present a mathematical description of high pressure processes in liquids at compressible conditions, quantifying the effect of density variations on the flow pattern due to those pressure variations. The improved mathematical approach is coupled to a Large Eddy Simulation (LES) solver. The main code was developed by OpenSource Ltd. for OpenFOAM, and the authors have introduced the additional expressions in order to calculate particular variables. For validating the code improvement, the LES solver is applied to a modern common-rail nozzle injector used in diesel engines. Results have been compared against other calculations that assumed constant properties and simultaneously validated with experimental data.

Fuzzy Diagnosis Module Based on Interval Fuzzy Logic: Oil Analysis Application

This paper presents the basic characteristics of a prototype fuzzy expert system for condition monitoring applications, in particular, oil analysis in Diesel engines. The system allows for reasoning under absent or imprecise measurements, providing with an interval-valued diagnostic of the suspected severity of a particular fault. A set of so-called metarules complements the basic fault dictionary for fine tuning, allowing extra functionality. The requirements and basic knowledge base for an oil analysis application are also outlined as an example.

Wear Rate Determination for IC Engine Condition Monitoring Results Obtained in an Urban Transport Fleet

This paper is structured into two different parts: Firstly, it describes a methodology to evaluate wear conditions in internal combustion engines in order to go beyond the classical evaluation based on specified wear concentration limits provided by engine manufacturers or commercial oil laboratories. The proposed methodology uses spectrometric wear debris measurement data and typical maintenance data to obtain a more representative parameter of wear condition, defined as compensated wear rate, that takes into account particular engine operating conditions affecting wear concentration measurements. Later, an evaluation of this compensated wear rate is carried out using statistical criteria and considering individual engine characteristics such as engine age, type of service, engine metallurgy, environmental conditions of work etc. Secondly, results obtained from an investigation carried out on oil samples from engines of an urban transport fleet are presented, confirming the value of compensated wear rate as a more representative parameter of engine wear behaviour during the oil use period than absolute concentration values.