Laser Doppler velocimetry measurement at a hard-to-reach intake port of a two-stroke engine

To understand better the complex scavenging process in ported two-stroke engines, optical set-ups were designed for velocity measurements at the exit of an intake port of a motoring and firing single-cylinder propane-fueled two-stroke engine by laser Doppler velocimetry. The radial velocity component was measured at the center of one port at engine speeds of 600, 900, and 1200 rpm. Laser beams entered the engine from the top through a quartz window and the light scattered by the seed particles was collected at 90° through the exhaust ports and a side window. The noise produced by the piston head was analyzed and separated from the signal generated by the seed particles. Analysis of the results from this engine showed that, in general, differences in both magnitude and the shape of the plotted results were observed when the engine was firing. A backflow into the intake system was observed at 600 rpm; this backflow decreased in strength, shifted in crank angle at 900 rpm, and eventually was eliminated at an engine speed of 1200 rpm.     

A chemical kinetic interpretation of the octane appetite of modern gasoline engines

Fuel anti-knock quality is a critical property with respect to the effective design of next-generation spark-ignition engines which aim to have increased efficiency, and lower emissions. Increasing evidence in the literature supports the fact that the current regulatory measures of fuel anti-knock quality, the research octane number (RON), and motor octane number (MON), are becoming decreasingly relevant to commercial engines. Extrapolation and interpolation of the RON/MON scales to the thermodynamic conditions of modern engines is potentially valuable for the synergistic design of fuels and engines with greater efficiency. The K-value approach, which linearly weights the RON/MON scales based on the thermodynamic history of an engine, offers a convenient experimental method to do so, although complementary theoretical interpretations of K-value measurements are lacking in the literature.This work uses a phenomenological engine model with a detailed chemical kinetic model to predict and interpret known trends in the K-value with respect to engine intake temperature, pressure, and engine speed. The modelling results support experimental trends which show that the K-value increases with increasing intake temperature and engine speed, and decreases with increasing intake pressure. A chemical kinetic interpretation of trends in the K-value based on fundamental ignition behaviour is presented. The results show that combined experimental/theoretical approaches, which employ a knowledge of fundamental fuel data (gas phase kinetics, ignition delay times), can provide a reliable means to assess trends in the real-world performance of commercial fuels under the operating conditions of modern engines.     

A mathematical model of Helmholtz resonator type gas oscillation discharges of two-stroke cycle engines

For the example of a one cylinder, 3·7 in³ two-stroke cycle engine, it is shown that combustion engines discharge combusted gas in oscillatory bursts whose primary frequency is independent of engine speed. The superposition of a Helmholtz resonator model and a thermodynamic model of the combustion process is used to predict pressure oscillations and sound radiation. It is shown that the elastic and inertial characteristics of the gas in the combustion chamber and the exhaust port have to be considered in the model. Theoretical and experimental results compare well.     

Laser metrology — a diagnostic tool in automotive development processes

Laser measurement techniques are widely used in automotive development processes. Applications at Volkswagen are presented where laser metrology works as a diagnostic tool for analysing and optimising complex coupled processes inside and between automotive components and structures such as the reduction of a vehicle's interior or outer acoustic noise, including brake noise, and the combustion analysis for diesel and gasoline engines to further reduce fuel consumption and pollution. Pulsed electronic speckle pattern interferometry (ESPI) and holographic interferometry are used for analysing the knocking behaviour of modern engines and for correct positioning of knocking sensors. Holographic interferometry shows up the vibrational behaviour of brake components and their interaction during braking, and allows optimisation for noise-free brake systems. Scanning laser vibrometry analyses structure-born noise of a whole car body for the optimisation of its interior acoustical behaviour.Modern engine combustion concepts such as in direct-injection (DI) gasoline and diesel engines benefit from laser diagnostic tools which permit deeper insight into the in-cylinder processes such as flow generation, fuel injection and spray formation, atomisation and mixing, ignition and combustion, and formation and reduction of pollutants. The necessary optical access inside a cylinder is realised by so-called ‘transparent engines’ allowing measurements nearly during the whole engine cycle. Measurement techniques and results on double-pulse particle image velocimetry (PIV) with a frequency-doubled YAG laser for in-cylinder flow analysis are presented, as well as Mie-scattering on droplets using a copper vapour laser combined with high-speed filming, and laser-induced fluorescence (LIF) with an excimer laser for spray and fuel vapour analysis.     

Soot elimination and NOx and SOx reduction indiesel-engine exhaust by a combination of discharge plasma and oildynamics

The soot in the exhaust gas from a 2-L diesel-engine car has been eliminated almost completely, independent of the load and cruising speed, by a plasma reactor mounted downstream of the engine exhaust and a novel technique using a combination of discharge plasma and oil dynamics. The NO_x (NO₂+NO) and SO_x components have also been reduced by about 70% at a rotational speed of 1200 rpm and a load of 7 kg-m, corresponding to about 60% of maximum torque (about 11.4 kg-m at 1200 rpm). The reduction rate of NO_x in this investigation is about 20% more efficient than ordinary treatment using a discharge plasma only     

Experimental investigation of in-duct insertion loss of catalysts in internal combustion engines

Acoustic performance characteristics of catalysts in the exhaust system are important in the development of predictive tools for the breathing system of internal combustion engines. To understand the wave attenuation behavior of these elements with firing engines, dynamometer experiments are conducted on a 3.0L V-6 engine with two different exhaust systems: one with the catalysts on the cross-over pipe, and the other that replaces the catalysts with equal length straight pipes. The instantaneous crank-angle resolved pressure data are acquired at wide open throttle and 500 rpm intervals over the operating range of the engine (from 1000 to 5000 rpm) at various locations in both exhaust systems. The effect of the catalyst is then isolated and discussed in terms of insertion loss at critical locations in the exhaust system. The analysis is presented both in terms of time-domain and order-domain. The predictive capability of a finite-difference based time-domain nonlinear approach is also demonstrated as applied to large amplitude waves in the exhaust system of firing engines.     

Waste heat recovery using looped heat pipes for air cooling

A scheme is described for the recovery of waste heat from stacks of gas turbine engines and the utilization of recovered energy for the cooling of ambient air. Relationships are summarized for the modeling of components of the cooling system. Samples are presented from performance data that is predicted by the model. Effect of size and design of system components, as well as operational variables on system performance, are discussed. It is concluded that the single most significant variable in the design of the looped heat-pipe recovery and utilization system is the geometry of the exhaust pipe of the gas turbine engine. Accordingly it is suggested that a design for the exhaust pipe of a gas turbine must consider the effects of (a) the variation of velocity of exhaust gases at different exhaust inlet temperatures, and the consequent pressure drops in the exhaust chimney pipe, and (b) the length of the exhaust pipe. The latter essentially determines the length of the heat pipe evaporator. Furthermore, the temperature drop through the air cooler is also significant, since this also influences system performance.     

Engines and exhaust after treatment systems for future automotive applications

Engine concepts for future automotive applicationsSafe, clean and efficient engines will become more important in modern societies where we will see higher levels of mobility on one hand and limited resources on the other hand. Gasoline engines for passenger cars have been developed to generate more power and reduce emissions at the same time. Therefore the engine systems have become complex with a number of subsystems.Because of its reliability and efficiency the diesel engine is classically operated in heavy duty vehicles, however in recent years because of its high torque when used with a turbocharger it has become more popular for passenger cars and even sport vehicles as well. The development of the diesel engine especially the direct injection as well as the common rail high pressure injection brought further improvement regarding power, efficiency and emissions. In the future exhaust after treatment systems will be developed in order to comply with emission standards similar to those of gasoline engines.Emission control systems with chemical and physical sensorsIn order to meet the more and more stringent emission regulations gasoline as well as diesel engines will need continuously improved exhaust after treatment systems. The options for the various applications are highlighted in the following.Today exhaust gas of gasoline engines is typically treated with “Three Way Catalysts” (TWC). The catalyst converts the pollutants CO, NO_X and Hydrocarbons into harmless compounds like CO₂, H₂O and N₂ by chemical reactions. Lambda-Sensors control the air fuel ratio of the engine and catalyst performance in order to get the best possible conversion of the pollutants.Modern lean burn engines have other options. Here the pollutants in the exhaust gases are only partially converted by a TWC function i.e. CO and Hydrocarbons. For the remaining NO_X a so called NO_X Storage Catalyst (NSC) is employed, which chemically stores NO and NO₂ during lean burn phase. For the conversion of stored NO_X the engine is periodically shifted to fuel rich operation. This more complex system is controlled with the help of mathematical catalyst models and by Lambda-, Temperature- and optionally NO_X-Sensors as well.Diesel engine exhaust of heavy duty vehicles will be treated with ammonia by Selective Catalytic Reduction (SCR) to reduce NO_X additionally to the catalytic oxidation of CO and Hydrocarbons. The ammonia is generated on board of the vehicle using harmless precursors like for example urea. For the control of this system Lambda-, Temperature- NO_X- and optionally NH₃-Sensors are employed.In addition to gaseous pollutants the particulate emissions from diesel engines will be removed by Diesel Particulate Filters (DPF). The system of oxidation catalyst and DPF is controlled by Temperature-, Pressure- and Particulate-Sensors.The mentioned highlights show that all three goals safe, clean and efficient can be met in the future by both gasoline and diesel engines combined with modern exhaust after treatment systems.     

Energy-exergy analysis of a diesel engine

An energy-exergy analysis for a diesel engine has been conducted. Both First and Second Laws of Thermodynamics are employed to take into account the quantity and quality of energy. The availability or exergy analysis based on the Second Law is utilized to identify the source of losses in useful energy within the components of diesel engines. This shows about 50% of the chemical availability of the fuel is destroyed due to uncounted factors and about 15% is lost in the cooling water or exhaust gases. On the other hand, the energy analysis shows 50% is wasted in the cooling water and exhaust gases and 15% is lost due to uncounted factors.     

An adaptive quarter-wave tube that uses the sliding-Goertzel algorithm for estimation of phase

This paper describes an adaptive quarter wave tube used to attenuate a tone from the exhaust noise of a large diesel engine. A sliding-Goertzel algorithm was used to calculate the phase angle of the transfer function between a microphone in the adaptive quarter wave tube and in the main exhaust duct. The control system adjusted the length of the adaptive quarter wave tube until the phase angle was −90° and caused the sound pressure level at the cylinder firing frequency in the exhaust duct to be minimized. The system was able to adapt to changes in engine speed, exhaust gas temperature, and load applied to the engine. The results demonstrate that the sliding-Goertzel algorithm can be used effectively to estimate the phase angle in an adaptive–passive acoustic control system.     

Measuring wave dynamics in IC engine intake systems

Wave dynamics in the intake system are known to strongly influence the performance of naturally aspirated internal combustion (IC) engines. Detailed measurements of the wave dynamics are required to optimize the performance of an engine, to validate the results of an engine performance simulation or to better understand the physics of the intake system. Five different methods for making such measurements are discussed in this paper. Four are based on different forms of pressure measurement and one uses hot-wire anemometry. The different methods are investigated by using results obtained on a single cylinder research engine. The different methods are used to produce measurements of fluctuating pressure and velocity as well as the specific acoustic impedance ratio of the intake pipe. Both time and frequency domain results are considered. The conclusion is that no single method is perfect or indeed universally applicable to all situations and in a typical investigation of wave action more than one method is likely to be used. The combined use of two methods, wave decomposition and an unusual bi-directional pitot-static tube, seems to offer a robust reliable and useful strategy for measuring wave dynamics in the intake pipe that should prove successful on most IC engines.     

Source identification of gasoline engine noise based on continuous wavelet transform and EEMD–RobustICA

In order to separate noise source of gasoline engine, ensemble empirical mode decomposition (EEMD), robust independent component analysis (RobustICA) and continuous wavelet transform (CWT) are applied to study the blind source separation and noise source identification of gasoline engine. After the signal is decomposed with EEMD into a set of intrinsic mode function (IMFs), RobustICA has been applied to extract independent sources. The combined technique alleviates the problem of mode mixing in EMD and overcomes the problem that the number of sensors must be larger than or equal to the number of separated components. At the same time, RobustICA’s cost efficiency and robustness are particularly remarkable for short sample length in the absence of pre-whiten. CWT using the Complex Morlet Wavelet (CMW) is used for its better time–frequency localization features to analyze time–frequency characteristics of the ICA results. Combining the time–frequency results with different noise sources frequency spectrums, the corresponding relation of the different noise sources of gasoline engine and the independent components is determined. It turns out that these independent components correspond to the exhaust, combustion and piston slap noise of the gasoline engine respectively.     

进气加入CO2对直喷式柴油机燃烧的影响

在直喷式柴油机上研究了进气加入CO2气体对其燃烧特性以及发动机性能和排放品质的影响.研究结果表明,进气加入CO2,柴油机的混合气形成过程几乎不受CO2气体加入量的影响,主要反映在着火延迟期随着CO2加入量的增加而变长,燃烧持续期缩短,燃烧最高温度降低.同时导致柴油机的最大爆发压力和压力升高率降低,并且其出现的位置后移,充气效率下降,排气温度上升.加入CO2后,NOx排放有较大下降,HC、CO稍有增加,烟度受到的影响不大.     

Prediction of intake noise of an automotive engine in run-up condition

It is very important to predict the radiated noise from the engine intake system for the effective noise control and virtual prototyping of in-cavity and outdoor noise of a vehicle. To this end, one should precisely measure the in-duct acoustic source parameters of the intake system, viz., source strength and source impedance. Usually, the noise radiation characteristics need to be expressed as a function of engine speed. In this study, acoustic source parameters of an engine intake system under engine run-up condition were measured by using the direct method. Direct method employed two external loudspeakers, turned on simultaneously, and three microphones for the separation of upstream and downstream wave components. It was noted that the frequency spectra of source impedance hardly changes with the increase of engine speed. Utilizing this fact, source strength under the engine run-up condition was calculated by assuming invariant source impedance. Predicted insertion loss and radiated sound pressure level using the measured source parameters were compared with those of measured data and predicted data using several idealized source models, which have been adopted for the calculations. A reasonably good agreement was observed between measured sound spectra at the intake orifice and predicted one using the measured source data. It was shown that the source data obtained by the present method yielded a far better prediction accuracy than those by the idealized source models.     

A survey of low velocity and coaxial jet noise with application to prediction

A review of recent published data on low velocity jet noise is given together with previously unpublished results taken from the Rolls-Royce Noise Research Programme on model rigs and full-scale engines. Noise correlations are given which show that at low jet velocities, the low frequency exhaust noise which is commonly referred to as jet noise, emitted from the fan stream of a turbofan engine is considerably lower in level than that from the (hot) centre stream. From this result, a new prediction procedure for coaxial jet noise of turbofan engines is then developed. Comparisons are given which show that this method gives good correlation with measured results from a number of full-scale turbofan engines. The importance of accurate estimation of the “ground reflection effect” is clearly demonstrated. A critical review of published jet noise data from model coaxial jets is given and the need for further extensive testing emphasized.     

In situ sensor for cycle-resolved measurement of temperature and mole fractions in IC engine exhaust gases

We present a multi-species mole fraction and temperature sensor for in situ exhaust gas diagnostic of internal combustion (IC) engines. The sensor is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) and incorporates four optical channels - two miniature White cells and two double-traversal cells - with base lengths of 6?cm. It has been demonstrated at a hot air test stand and in the exhaust manifold of a single-cylinder research engine, with measured temperatures of up to 1000?K. Stable operation was achieved with absorption lengths of up to 192?cm (test stand) and 97?cm (engine). Employing time-division multiplexed detection, six species were measured simultaneously in the engine exhaust, at wavelengths ranging from 1.4?µm to 5.2 µm: water vapor (H₂O), carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄), nitrogen dioxide (NO₂) and nitric oxide (NO). The effective measurement rate was as high as 1?kHz, and cycle-to-cycle variations were clearly detected. We show the correlation of the air-fuel equivalence ratio with the spectroscopically measured mole fraction of each species. At a cycle-resolved rate, detection limits for the legally regulated species NO and NO₂ were 1?ppm and 4?ppm, respectively. The sensor is intended to help improve the understanding of IC engine emission behavior during fast transients.     

Effect of manifold design and firing order on the short term spectrum

Separation by homomorphic filtering of the engine speed dependent harmonics from the remaining components of a vehicle's acoustic emission involves selection of the optimum quefrency for the filter. This requires an understanding of the formation, on the short term log power spectrum, of harmonics of both the fundamental frequency from successive cylinder firings and also the frequency from firings of the same cylinder. It is shown that these harmonics depend on the combination of the design of the engine's exhaust manifold and on the cylinder firing order. Comparisons are made between the engine harmonics displayed from segments of time series containing different numbers of crankshaft rotations. Finally graphs are included where meaningful comparison can be made between homomorphed spectra of two different vehicles of the same type. As a result of this investigation an explanation is offered which resolves the problems encountered by workers analysing engine related harmonics.     

Influence of Intake/Exhaust Channel Lateral Profiling on Thermomechanics of Pulsating Flows

The hypothesis that pipeline lateral profiling can be used to regulate pulsating flows in the air-gas systems of energy machines is tested. The results of the physical simulation of gas dynamics and local heat transfer in the intake and exhaust channels of various configurations in the piston internal combustion engine in the conditions of gas-dynamic nonstationarity are presented. We have established that the lateral profiling of intake and exhaust pipes promotes the stabilization of gas flows in the air-gas systems of the engine, and decreases the intensity of the local heat transfer by up to 30%, depending on the initial conditions.     

LCD投影系统光学引擎的计算机仿真分析

光学引擎是决定LCD投影系统色度、光度品质的核心部件之一。根据投影系统光学引擎的结构特点，结合色度学原理，利用光路追踪法编制了光学引擎的色度、光度仿真分析软件。仿真分析软件具有双向功能：对引擎的光学系统可进行色度光度计算，并可根据色度、光度指标优化光学引擎结构。将仿真与实际的光学引擎进行了对比实验，得到多组投影视场的色坐标对比数据，最后用软件优化了一个光学引擎，得到该引擎结构的优化数据。实验结果表明：该软件可提高光学引擎的设计效率。