In the current work, the combustion process inside a stratified pre-chamber ignition system is analyzed. The pre-chamber is installed on a Rapid Compression-Expansion Machine (RCEM) and runs at different combinations of fuel-air equivalence ratio in the main chamber as well as in the pre-chamber, which is controlled by a fuel injection during the compression stroke. In order to analyze the results in detail, a zero-dimensional model for the pre-chamber is proposed. First, a K-k-ϵ model is developed and calibrated according to three-dimensional simulations in motoring conditions performed in a Computational Fluid Dynamic solver (Converge). Then, a thermodynamic model including the mass exchange between both chambers as wells as the heat transfer losses to the walls is used to compute the instantaneous heat release rate in the pre-chamber. Both pieces of information are combined to evaluate the effective flame propagation speed, and also to decouple the effects in terms of laminar flame speed, turbulence-flame interaction and gas velocity due to expansion effects in the burned products. The flame speed values obtained are consistent when the equivalence ratio in the pre-chamber is maintained, regardless the conditions in the main chamber, while a significant deterioration is seen once lean operation appears in the pre-chamber. Finally, the flame speed is compared to an average propagation speed estimated from broadband chemiluminescence visualization tests, showing good consistency with the model predictions.

The automotive industry is driven its efforts to cleaner internal combustion engines. As a result, the engine has become conditioned by the exhaust aftertreatment systems. The regeneration of wall-flow particulate filters (PFs) evidences such an interaction. The PFs prevent the soot emission whereas, as a counterpart, the fuel consumption increases. Consequently, passive and active regeneration strategies are needed to clean the filter back and limit the penalty in CO2. In this context, modelling tools play a key role to achieve a comprehensive understanding and control of the regeneration. In this work, a regeneration model coupled to a one-dimensional compressible unsteady flow solver for PFs is presented. The importance of the main physical and chemical steps related to the soot oxidation is discussed. The influence of the diffusion of gaseous reactants inside the primary soot particles is firstly addressed. The inclusion of this step into the definition of the reaction rate provides temperature dependence to the soot specific surface. Next, the reactants adsorption is analysed. This step leads to define a surface coverage, which behave as an equivalent reaction order. It allows figuring out the influence of the gaseous reactants concentration on the reaction rate and its dependence with the temperature.

This paper addresses the optimal control of a long-haul passenger train to deliver minimum-fuel operations. Contrary to the common Pontryagin minimum principle approach in railroad-related literature, this work addresses this optimal control problem with a direct method of optimization, the use of which is still marginal in this field. The implementation of a particular direct method based on the Euler collocation scheme and its transcription into a nonlinear problem are described in detail. In this paper, this optimization technique is benchmarked with well-known optimization methods in the literature, namely dynamic programming and the Pontryagin minimum principle, by simulating a real route. The results showed that the direct methods are on the same level of optimality compared with other algorithms while requiring reduced computational time and memory and being able to handle very complex dynamic systems. The performance of the direct method is also compared to the real trajectory followed by the train operator and exhibits up to 20% of fuel saving in the example route.

Optimizing the average annual cost of a bus fleet has become an increasing concern in transport companies management around the world. Nowadays, there are many tools available to assist managerial decisions, and one of the most used is the cost analysis of the life cycle of an asset, known as "life cycle cost''. Characterized by performing deterministic analysis of the situation, it allows the administration to evaluate the process of fleet replacement but is limited by not contemplating certain intrinsic variations related to vehicles and for disregarding variables related to exigencies of fleet use. The main purpose of this study is to develop a combined model of support to asset management based in the association of the life cycle cost tool and the mathematical model of Monte Carlo simulation, by performing a stochastic analysis considering both age and average annual mileage for optimum vehicle replacement. The utilized method was applied in a Spanish urban transport fleet, and the results indicate that the use of the stochastic model was more effective than the use of the deterministic model.

CO 2 emissions and fuel consumption reduction in road transportation has become one of the most relevant concerns either for governments, OEMs and final users, especially fleet owners and managers, led mainly by global warming and rising fuel prices concerns.For vehicles driven by internal combustion engines (ICE) the fuel consumption rates are directly related to CO 2 emissions, the latter being a consequence and an efficiency indicator.A wide variety of solutions have arisen to overcome this challenge ranging from hybridization to changes in the vehicledesign looking for more aerodynamic profiles, to solutions like eco-driving courses for drivers or the usage of alternative fuels such as biofuels.All of these solutions vary in technical complexity, implementation costs and terms.One proven cost-effective way to reduce the fuel consumption is the use of low viscosity oils (LVO) in order to reduce the engine inner friction, reducing by this way the amount of energy required to move the engine parts resulting this in a fuel consumption reduction.This paper presents a study where the effect of the use of LVO on urban transport buses on the CO2 fleet spot and fuel consumption, based on a comparative test where 39 buses worked for nearly a year separated in two groups each of them carrying either LVO or standard viscosity oils.

This article describes a methodology for the optimization of a bottoming cycle as a waste heat recovering system in vehicles. The methodology is applied to two particular cases in order to evaluate the preliminary energetic and technical feasibility of the implementation of a bottoming cycle in a heavy duty diesel (HDD) engine considering two different criteria. Initially, a study of the different waste heat sources of the engine is described. In this study, the power and exergy of each heat source is quantified, in order to evaluate which sources are suitable to be used in the bottoming cycle. The optimum working fluids to run the cycles are selected (water and R245fa). Then, the ideal Rankine cycle is optimized for the two different working fluids and different sets of heat sources (all the available heat sources and the sources with high exergy respectively) throughout the engine operating range, reaching a maximum improvement of 15% of the fuel consumption of the engine. Later, a study of the minimum temperature difference between the hot and cold flow of the heat exchangers is described. The improvements in fuel consumption and the size of the installed heat exchanger are related to this temperature difference. Finally, the non-ideal behavior of the machines (pump and expander) is analyzed, obtaining a maximum improvement of 10% in brake specific fuel consumption (bsfc).

Considerable efforts have been devoted to the development of predictive models that, from a certain set of data related to an engine, and making use of an adequate representation of the effect of the silencing elements, provide an estimate of the exhaust noise emitted. Such models should allow for the consideration of the engine and its interaction with the exhaust system. This is properly achieved by gas-dynamic models, which are becoming the standard, but linear models solved in the frequency domain and representing the engine as a linear time-invariant source may still play a role in exhaust system design, as the engine is treated as a black box. Such a representation is very attractive for engine manufacturers, since it gives the possibility to provide data on the engine without any possibility to trace back to its real characteristics. In order to provide additional criteria for the suitability of the application of a linear time-invariant representation to an engine exhaust, in this paper a multi-load method has been used to extract source characteristics from gas-dynamic simulation results. The details of the method, in which the resulting over-determined system is solved by fitting the values of the source parameters in a least-squares sense, are described, and different approaches are used in order to check the internal consistency of the source representation: the identification of pressure and velocity sources, and the application of the least-squares criterion to the modulus or to the real and imaginary parts separately. In particular, eight different determinations of the source impedance are obtained and, considering the application of the formalism to an engine exhaust, the differences observed provide a suitable criterion for the evaluation of the suitability of the representation and of the particular set of loads chosen.

ABSTRACTThis work presents a comparative assessment of engine oil performance on field test using urban transport vehicles powered by compressed natural gas engines using two different mineral oil formulations approved by engine manufacturer. The first one is considered as a baseline reference, and the second one is a higher quality formulation in terms of base stock refining and additive content. Higher quality oil has shown a significant enhanced lubricant performance, leading to reach the oil drain interval defined by engine manufacturer on these engines without penalties in maintenance costs.In order to assess oil performance, an oil analysis programme has been established for oil samples collected from vehicles operated under real service conditions in an urban transport fleet. Monitored parameters include oxidation, nitration, aminic anti‐oxidant additives depletion, anti‐wear additives depletion, total acid number, total basic number and remaining useful life number (as an estimation of anti‐oxidant additive depletion including aminic and zinc dialkyldithiophosphate).Results obtained in more than 90 samples from 15 different vehicles have shown higher degradation rates for low quality lubricant oil formulation. This deviation can be explained taking into account factors related with lower anti‐oxidant additives content and lower thermal stability that can be mainly related with the base stock quality. This lower oil performance can be finally converted into higher vehicle maintenance cost and lower engine reliability. Copyright © 2013 John Wiley & Sons, Ltd.

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 wave number 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.

In this article, two of the most used methods for diesel spray macroscopic characterization are presented; the first one is the likelihood ratio test method (LRT) and the second one isthe Otsu’s thresholding method(OTM). Both methodsare applied to different diesel sprays visualized in a high-pressure nitrogen chamber obtaining better results with the LRT in terms of both contour determination and coherence of the results. Finally, the influence of the algorithm used for the segmentation on the macroscopic characterization measurements is observed.

PurposeThe purpose of this paper is to develop a methodology for audit maintenance strategies and processes focused in urban transport fleets.Design/methodology/approachIn response to this purpose, the main objective is to identify the strengths and the weaknesses of the maintenance system in order to establish actions that minimize the weaknesses and maximise the strengths. To audit properly, a well‐structured methodology is required, in which analyses will be performed, from general to more specific plans and procedures.FindingsIt was found that the evaluation of other related aspects is also necessary. Aspects such as: facilities, personnel, computerised information systems and the accurate management of the information derived from the proper maintenance activities.Practical implicationsUsing the methodology described in this paper will make it easier for the company to evaluate real maintenance performance and possible improvements.Originality/valueBy using this methodology, a detailed situation of the fleet's maintenance is illustrated, and consequently different operations can be taken into account to achieve the established improvement objectives

This paper presents a non-intrusive fault detection technique, based on the analysis of rolling block oscillations, assuming that the engine behaves as a rigid body mounted on elastic supports. Engine diagnosis is feasible with a single accelerometer, which constitutes an attractive procedure for maintenance engineers. The proposed method is illustrated with modelled and measured results obtained with two different automotive engines. The engine diagnosis is performed using a particular normalisation of the Fast Fourier Transform. The procedure leads to identify multiple sub-harmonics of the firing frequency which allow a reliable diagnosis.

Expert systems have been used in condition monitoring for many years. The implementation and use of these systems have met with varying degrees of success. This paper presents a prototype fuzzy logic-based expert system for condition monitoring applications, in particular, diesel engines oil analysis diagnosis. The system allows for reasoning under incomplete or imprecise measurements, providing an interval valued diagnostic of the suspected severity of a particular engine fault. A set of so-called metarules complements the basic fault dictionary for fine tuning, allowing extra functionality.

Conventional misfire diagnosis techniques are based on the analysis of the instantaneous engine speed. Although they have proved their efficiency in some operating conditions and for the detection of total misfires, their performance could be insufficient in a near future. This paper presents a comparative study of different alternative detection principles for the detection of slight unevenness between cylinders in the injection process for a turbocharged Diesel engine. The selected techniques are the instantaneous exhaust manifold pressure, the instantaneous turbocharger speed and the mean temperature at the exhaust cylinder ports. All alternative techniques show improved performance and linearity compared to the conventional one, particularly at high engine speed and low load. All these techniques are compared with the conventional approach and main advantages and disadvantages are discussed.

This work presents the development of a method which analyzes metallic wear debris and contaminants found to be present in fuels used by Diesel engines. The particles have been isolated by following two complementary methods; firstly, a magnetic separation method and then a filtering method using membranes. Particles are subsequently characterized by means of optical and electron microscopy, where it is possible to establish the type and severity of the wear, as well as establishing how the mechanism parts are actually affected by wear. This technique allows a predictive maintenance of the fuel injection systems to be carried out, as it allows for possible breakdowns to be detected prior to a serious failure being produced.

Combustion failure diagnosis techniques for reciprocating internal combustion engines have been developed over the last few years. Nowadays the most usual techniques are based on the crankshaft instantaneous speed or on engine vibrations. These methods, although successfully in use, may be applied only to maintenance tasks or to low and moderate engine speeds. In this paper, a controller for the correction of injection failures is presented. The aim of the algorithm is to ensure that the same quantity of fuel is injected into each one of the cylinders. This governor can be applied to the full operating range of the engine. The injection failure detection and identification technique is based on the measurement of the turbocharger instantaneous speed and its treatment in the frequency domain. The simulation of the controller shows an effective reduction in the dispersion between cylinders to a level below 2 per cent.

In internal combustion engines, instantaneous exhaust pressure measurements are difficult to perform in a production environment. The high temperature of the exhaust manifold and its pulsating character make its application to exhaust gas recirculation control algorithms impossible. In this paper an alternative method for estimating the exhaust pressure pulsation is presented. A numerical model is built which enables the exhaust pressure pulses to be predicted from instantaneous turbocharger speed measurements. Although the model is data based, a theoretical description of the process is also provided. This combined approach makes it possible to export the model for different engine operating points. Also, compressor contribution in the turbocharger speed pulsation is discussed extensively. The compressor contribution is initially neglected, and effects of this simplified approach are analysed.