José M. Desantes

Combining Neural Networks and Genetic Algorithms to Predict and Reduce Diesel Engine Emissions

Diesel engines are fuel efficient which benefits the reduction of CO2 released to the atmosphere compared with gasoline engines, but still result in negative environmental impact related to their emissions. As new degrees of freedom are created, due to advances in technology, the complicated processes of emission formation are difficult to assess. This paper studies the feasibility of using artificial neural networks (ANNs) in combination with genetic algorithms (GAs) to optimize the diesel engine settings. The objective of the optimization was to find settings that complied with the increasingly stringent emission regulations while also maintaining, or even reducing the fuel consumption. A large database of stationary engine tests, covering a wide range of experimental conditions was used for this analysis. The ANNs were used as a simulation tool, receiving as inputs the engine operating parameters, and producing as outputs the resulting emission levels and fuel consumption. The ANN outputs were then used to evaluate the objective function of the optimization process, which was performed with a GA approach. The combination of ANN and GA for the optimization of two different engine operating conditions was analyzed and important reductions in emissions and fuel consumption were reached, while also keeping the computational times low

Measurements of Spray Momentum for the Study of Cavitation in Diesel Injection Nozzles

In Diesel injection Systems, cavitation often appears in the injection nozzle holes. This paper analyses how cavitation affects the Diesel spray behavior. For this purpose two spray parameters, mass flux and momentum flux, have been measured at different pressure. We know that cavitation brings about the mass flux choke, but there are few studies about how the cavitation affects the momentum and the outlet velocity. The key of this study is just the measurement of the spray momentum under cavitation conditions.

Modified impulse method for the measurement of the frequency response of acoustic filters to weakly nonlinear transient excitations

In this paper, a modified impulse method is proposed which allows the determination of the influence of the excitation characteristics on acoustic filter performance. Issues related to nonlinear propagation, namely wave steepening and wave interactions, have been addressed in an approximate way, validated against one-dimensional unsteady nonlinear flow calculations. The results obtained for expansion chambers and extended duct resonators indicate that the amplitude threshold for the onset of nonlinear phenomena is related to the geometry considered.

Estimation of velocity fluctuation in internal combustion engine exhaust systems through beamforming techniques

The knowledge of the particle velocity fluctuations associated with acoustic pressure oscillation in the exhaust system of internal combustion engines may represent a powerful aid in the design of such systems, from the point of view of both engine performance improvement and exhaust noise abatement. However, usual velocity measurement techniques, even if applicable, are not well suited to the aggressive environment existing in exhaust systems. In this paper, a method to obtain a suitable estimate of velocity fluctuations is proposed, which is based on the application of spatial filtering (beamforming) techniques to instantaneous pressure measurements. Making use of simulated pressure-time histories, several algorithms have been checked by comparison between the simulated and the estimated velocity fluctuations. Then, problems related to the experimental procedure and associated with the proposed methodology are addressed, making application to measurements made in a real exhaust system. The results indicate that, if proper care is taken when performing the measurements, the application of beamforming techniques gives a reasonable estimate of the velocity fluctuations.

Large-eddy simulation analysis of the influence of the needle lift on the cavitation in diesel injector nozzles:

The cavitation phenomenon has a strong influence on the internal flow and spray development in diesel injector nozzles. Despite its importance, there are many aspects which still remain unclear, especially for partial needle lifts when the injector is in the opening and closing phases. For that reason, the current paper is focused on the influence of the needle lift on the internal flow in a diesel nozzle. This study was carried out with three-dimensional simulations at a high injection pressure (160 MPa) using a homogeneous equilibrium model implemented in OpenFOAM to model the cavitation phenomenon. The nozzle was simulated with large-eddy simulation methods at six different needle lifts (10 μm, 30 μm, 50 μm, 75 μm, 100 μm and 250 μm), providing relevant information about the evolution of the internal flow, the turbulence development (the vorticity, the turbulence–cavitation interaction and the turbulent structures) and the flow characteristics in the nozzle outlet (the mass flow, the momentum flux and the effective velocity) with the needle position.

The development of a semi-empirical model for rapid NOx concentration evaluation using measured in-cylinder pressure in diesel engines:

Continued legislative pressure to reduce NO x emissions from diesel engine combustion systems generates a desire for cycle-by-cycle emissions data, with a view to their use in a feedback control strategy, perhaps in conjunction with an exhaust catalytic reactor. While NOx sensors that provide fast, robust, reliable, and continuous measurements in a diesel exhaust at a reasonable price are currently the subject of much development, the present work focuses on an indirect approach. This has led to the development of a semi-empirical model that can be used to estimate NO x emissions, based on more easily measured input data, primarily in the form of instantaneous in-cylinder pressure as a function of crank angle. The model computations are based on fundamental thermodynamic principles, but key empirical constants have been derived with the aid of statistical techniques. The approach taken relied on the availability of an extensive bank of experimental data from three different designs of direct injection diesel engine, each utilizing common rail type fuel injection systems and, in some cases, with the use of multiple injections per cycle.

Methodology for measuring exhaust aerosol size distributions using an engine test under transient operating conditions

A study on the sources of variability in the measurement of particle size distribution using a two-stage dilution system and an engine exhaust particle sizer was conducted to obtain a comprehensive and repeatable methodology that can be used to measure the particle size distribution of aerosols emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement method; an evaluation of the influence of sampling factors, such as dilution system pre-conditioning; and a study of the effects of the dilution conditions, such as the dilution ratio and the dilution air temperature. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a highly reliable measurement methodology that could be applied to further studies on the effect of engine operating parameters on exhaust particle size distributions.

On the combination of high-pressure and low-pressure exhaust gas recirculation loops for improved fuel economy and reduced emissions in high-speed direct-injection engines

In this paper, an experimental study of the combination of low-pressure and high-pressure exhaust gas recirculation architectures has been carried out. In the first part of the paper, the effects of both high-pressure and low-pressure exhaust gas recirculation architectures on engine behaviour and performance are analysed by means of a series of steady tests. In the second part, the effects of the combination of both architectures are addressed. The results show that the low-pressure configuration improves high-pressure exhaust gas recirculation results in brake-specific fuel consumption, nitrogen oxides and exhaust gas opacity; nevertheless, hydrocarbon emissions are increased, especially during the engine warm up. In addition, the exhaust gas recirculation rate achieved with low-pressure systems is limited by the pressure difference between diesel particulate matter outlet and compressor inlet; therefore, the high-pressure system can be used to achieve the required exhaust gas recirculation levels without increasing pumping losses. In this sense, the combination of both exhaust gas recirculation layouts offers significant advantages to reduce emissions and fuel consumption to meet future emission requirements.

Evaluation of the Thermal NO formation mechanism under low-temperature diesel combustion conditions

Over the past two decades, the amount of exhaust gas pollutants emissions has been significantly reduced due to the severe emission legislation imposed in most countries worldwide. Initial strategies simply required the employment of simple after-treatment and engine control devices; however, as the restrictions become more stringent, these strategies are evolving in the development of different combustion modes, specially characterized by having low-temperature combustion characteristics. These new working conditions demand the need to check the suitability of the current NO predictive models that coexist nowadays under standard diesel combustion characteristics, paying closer attention to the Thermal mechanism. In order to do so, a common chemical-kinetic software was employed to simulate, for n-heptane and methane fuels, fixed local conditions (standard diesel and low-temperature combustion) described by constant pressure, relative mixture fraction, oxygen mass fraction and initial and final reaction temperature. The study reflects a common trend between all the studied cases, independently of the considered local conditions, making it applicable to more complex situations such as real NO formation processes in diesel sprays. This relationship was characterized by a fourth-degree polynomial equation capable of substantially improving the NO prediction by just using the Thermal NO predictive model.

Evaluation of the non-steady flow produced by intake ports of direct injection Diesel engines

The most usual way to characterize a D.I. Diesel engine cylinder head is based on steady flow tests with fixed pressure drop across the valve and at different valve lifts. A discharge coefficient and a swirl number are defined, which are representative of the breathing capacity and angular velocity generation of the intake system. A question arising is the validity of such parameters in non-steady conditions, with time scales similar to those of the firing engine, where the valve is moving and the pressure drop across the valve is time dependent. Experimental tests were conducted both in steady and non-steady flow test rigs in order to assess the quasi-steady assumption in terms of the mass flow rate across the valve, as well as swirl produced by the intake port. Time resolved laser-Dopplervelocimetry was used, together with an extension of a conventional test flow rig to non-steady operation.