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.     

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.     

The influence of the exhaust system unsteady gas flow and insulation on the performance of a turbocharged diesel engine

A comprehensive digital computer program is used to simulate the unsteady gas flow in the exhaust and inlet systems of a multi-cylinder, turbocharged, medium-high speed, four-stroke diesel engine installed at the authors' laboratory. The simulation assumes one-dimensional, time-varying gas flow in the engine pipes and incorporates numerous realistic fluid dynamic, thermodynamic and heat-transfer features. The characteristic mathematical transformation solution of the gas-flow dynamics partial differential equations is interfaced with First-Law analysis models of the cylinders main chambers and prechambers. The simulation results are compared most favourably against the engine's experimental performance results, which include mean air consumption rate, pressure histories at various locations on the exhaust system, and energy-mean temperature values at the exit of the exhaust system. The simulation results are also utilized for the determination of the various cylinders' exhaust waves intensity, as they are imposed by the design characteristics of the exhaust manifold. The plotting of relevant charts, showing the contour variation of gas pressure, temperature and Mach index against engine crank angle and pipe length, aids the correct interpretation of the observed behaviour. The detailed simulation of the fluid dynamic and heat-transfer fields in the engine exhaust system, permits an interesting parametric study of the influence of the degree of insulation of the exhaust system on the energy and exergy (availability) content of the exhaust gases before the turbocharger turbine, by coupling the above First-Law with Second-Law analysis concepts.     

Measurement of the effect on brake performance of the intake and exhaust system components in a motorbike high speed racing engine

The paper presents a series of brake performance measurements for a high speed Road Racing Supersport motorbike engine. A modular approach consisting in a progressive assembling of each component belonging to the intake and exhaust systems is used to investigate the influence of these components on volumetric efficiency through brake torque chassis dynamometer tests. In spite of the design effort that is usually made to keep the cylinder air intake independent of each other in this kind of engines, results showed a considerable acoustic coupling between the intake primary manifolds and the upstream components. Moreover, a good correspondence is found about intake and exhaust tuning regimes between experimental results and analytical relationships proposed in the literature. The presented results can also be interpreted as representative for the overall very high speed engines category (including MotoGP and F1 ones), being the air-breathing system layout mostly independent of engine technological level within this category.     

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.     

Predictions and experimental studies of the tail pipe noise of an automotive muffler using a one dimensional CFD model

The tail pipe noise from a commercial automotive muffler was studied experimentally and numerically under the condition of wide open throttle acceleration in the present research. The engine was accelerated from 1000 to 6000 rpm in 30 s at the warm up condition. The transient acoustic characteristics of its exhaust muffler were predicted using one dimensional computational fluid dynamics. To validate the results of the simulation, the transient acoustic characteristics of the exhaust muffler were measured in an anechoic chamber according to the Japanese Standard (JIS D 1616). It was found that the results of simulation are in good agreement with experimental results at the 2nd order of the engine rotational frequency. At the high order of engine speed, differences between the computational and experimental results exist in the high revolution range (from 5000 to 6000 rpm at the 4th order, and from 4200 to 6000 rpm at the 6th order). According to these results, the differences were caused by the flow noise which was not considered in the simulation. Based on the theory of one dimensional CFD model, a simplified model which can provide an acceptable accuracy and save more than 90% of execution time compared with the standard model was proposed for the optimization design to meet the demand of time to market.     

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.     

A study on generation of noise by high-speed pulsating jets

This paper describes the noise generation in an exhaust system of a reciprocating engine and focuses on the noise generated by shock/vortex interaction. The pulsating flow through the exhaust pipe consists of the compression and expansion wave, shock wave being generated by the non-linearity of the compression wave at its head. The jet noise is produced when the pulsating flow is discharged from the pipe end into atmosphere. The numerical simulation based on a finite difference method and experiment were made, the result of both of them being compared. First, the flow field in the pipe was obtained to easily discuss the characteristic of the pulsating jet in terms of the pressure history in the pipe. The jet structure was visualized by using schlieren and shadowgraph techniques. Sound pressure measurements at various locations were made in order to survey the directivity of the noise. The comparison between the result of numerical calculation and experiment showed a good agreement. A noise source related to shock/vortex interaction was confirmed by the numerical study clearly.     

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     

Laser induced fluorescence and flame photography-Tools in gasoline engine combustion analysis

The development of engine combustion systems aims at exploiting the targets set by thermodynamics within the constraints of practical mechanical systems. This, in particular, involves the supply of a combustible mixture, its ignition and combustion. The fluid dynamic and thermo-chemical processes involved therein must be controlled in a way to provide: a temporal rate of heat release prescribed by thermodynamic, mechanic and acoustic requirements; the paths for ‘clean combustion’, i.e. the limitation of exhaust components such as nitric oxide, carbon monoxide or unburned hydrocarbons at lowest possible levels; and the cycle-to-cycle stability of the entire combustion process.

The engineering tasks to influence and control these processes create the permanent need to provide and improve diagnostic tools in order to understand the fluid dynamic and thermo-chemical phenomena governing the combustion in engines. It is the purpose of this article to describe the application of optical methods such as laser-inducedfluorescence and combustion photography for the investigation of cylinder filling, mixture formation and flame propagation in gasoline engines.

First, some diagnostic requirements for combustion analysis will be addressed. Optical techniques and experimental procedures are then derived and finally the application of these techniques in the analysis and development of gasoline engine combustion systems is demonstrated.     

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.     

Use of MHD systems in hypersonic aircraft

The possibilities of using magnetohydrodynamic (MHD) systems on hypersonic aircraft are discussed. The distinctive features of using MHD systems in the flow path of ramjet engines are examined. A quasi-one-dimensional mathematical model for the engine is presented which includes the MHD interaction with the flow. It is shown that the specific impulse of an engine system can be raised by using MHD systems. Zh. Tekh. Fiz. 68, 43–47 (November 1998)     

A hybrid approach for aeroacoustic analysis of the engine exhaust system

This paper presents a new hybrid approach for prediction of noise radiation from engine exhaust systems. It couples the time domain analysis of the engine and the frequency domain analysis of the muffler, and has the advantages of both. In this approach, cylinder/cavity is analyzed in the time domain to calculate the exhaust mass flux history at the exhaust valve by means of the method of characteristics, avoiding the tedious procedure of interpolation at every mesh point and solving a number of equations simultaneously at every junction. This is done by making use of an interrelationship between progressive wave variables of the linear acoustic theory and those of the method of characteristics. In this approach, nonlinear propagation in the exhaust pipe is neglected and free expansion is assumed at the radiation end of the exhaust pipe. In the case of a muffler proper, expansion from the exhaust pipe into the first chamber is assumed to be a free expansion. Various results of this approach are compared with those of the method of characteristics and the classical acoustic theory, and various peaks and troughs in insertion loss curves are analytically validated.     

Multi-lognormal soot particle size distribution for time-resolved laser induced incandescence in diesel engines

In-cylinder and exhaust soot particle size measurements were carried out using time-resolved laser induced incandescence and electrical mobility spectrometer techniques in a single cylinder optical diesel engine and multi-cylinder high-speed diesel engine. The temporal decay of the laser induced incandescence signal from a polydisperse nanoparticle ensemble of soot during transient diesel combustion is shown to be described by both a single-lognormal distribution as well as multi-lognormal size distribution. However, a multi-lognormal particle size distribution is introduced in the existing model for a comprehensive characterisation and realistic reconstruction of the size distribution. Detailed theoretical analysis of multi-lognormal size distribution along with its application to the experimentally measured soot particle size is validated in this work. These results were also qualitatively compared and independently verified by the experimental results obtained by the electrical mobility spectrometer and published transmission electron microscopy data. These findings reveal that the in-cylinder and the exhaust soot particle size distributions in engines are better represented by a multi-lognormal size distribution.     

Simulation of spray development and turbulent combustion processes in low and high speed diesel engines by the CMC-ISR model

Simulation is performed to analyse the characteristics of turbulent spray combustion in conventional low and high speed diesel engine conditions. Turbulence–chemistry interaction is resolved by the Conditional Moment Closure (CMC) model in the spatially integrated form of an Incompletely Stirred Reactor (ISR). After validation against measured pressure traces, characteristic length and time scales and dimensionless numbers are estimated at the locations of sequentially injected fuel groups. Conditional flame structures are calculated for sequentially evaporated fuel groups to consider different available periods for ignition chemistry. Injection overlaps the combustion period in the high rpm engine, while most combustion occurs after injection and evaporation are complete in the low rpm engine. Ignition occurs in rich premixture with the initial peak temperature at the equivalence ratio around 2–4 as observed in Dec [2]. It corresponds to the most reactive mixture fraction of the minimum ignition delay for the given mixture states. Combustion proceeds to lean and rich sides in the mixture fraction space as a diffusion process by turbulence. The mean scalar dissipation rates (SDRs) are lower than the extinction limit to show stability of diffusion flames throughout the combustion period.     

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.     

1+1/2对转涡轮设计及控制方法探索

本文对 1 1/2对转涡轮试验件进行了详细设计,并对其控制问题进行了初步探讨,结果表明所设计 1 1/2对转涡轮基本达到设计要求,其控制问题由高压静叶可调和尾喷管面积调节共同解决。     

Two case studies of cogeneration systems design and economic feasibility

Cogeneration is an ideal method of power production for applications which require both heat and power simultaneously, hence the name combined heat power (CHP). In this paper, design studies of cogeneration systems for two specific applications are presented. The results indicate the economic feasibility of such installations and how much energy can be saved, especially if the system is analysed on a long-term basis. It is shown that an essential requirement for cogeneration is the proper matching of power and heat demands.The first design study is of a combined power and heating system for a small suburban hospital which requires both steam and power for its various needs. The cogeneration system which was designed for this application consisted of a conventional turbo-charged spark ignition engine with heat exchange from its exhaust and engine cooling systems, coupled with an existing boiler. When the cogeneration system is inadequate to meet the electricity demands, the excess power would be bought from the grid supply. For an initial outlay of approximately $250,000 (1990 prices), an annual saving of $140,000 was conservatively predicted, with an internal rate of return of some 40% over 15 yr.The second design study is for the energy system of a large sugar confectionery factory with power and heat requirements, mainly for lighting, air conditioning and several manufacturing processes. The hardware which was chosenfor the cogeneration system for this case comprises a diesel engine converted for use with natural gas connected to a vertical shell and tube exhaust gas boiler. For an initial investment of approximately $700,000, an annual saving of about $130,000 (1991 prices) is predicted for a 10–15 yr project. The savings and the payback period depend on the electricity buy-back tariffs and the company's plans for future expansion.     

Infrared borescopic characterization of corona and conventional ignition for lean/dilute combustion in heavy-duty natural-gas engines

Natural gas (NG) is attractive for heavy-duty (HD) engines for reasons of cost stability, emissions, and fuel security. NG requires forced ignition, but conventional gasoline-engine ignition systems are not optimized for NG and are challenged to ignite mixtures that are lean or diluted with exhaust-gas recirculation (EGR). NG ignition is particularly difficult in large-bore engines, where it is more challenging to complete combustion in the time available. High-speed infrared (IR) in-cylinder imaging and image-derived quantitative metrics were used to compare two ignition systems in terms of the early flame-kernel development and cycle-to-cycle variability (CCV) in a heavy-duty, natural-gas-fueled engine that had been modified to enable exhaust-gas recirculation and to provide optical access via borescopes. Imaging in the near IR and short-wavelength IR yielded strong signals from the water emission lines, which acted as a proxy for flame front and burned-gas regions while obviating image intensification (which can reduce spatial resolution). The ignition systems studied were a conventional system and a high-frequency corona system. The air/fuel mixtures investigated included stoichiometric without dilution and lean with EGR. The corona system produced five separate elongated, irregularly shaped, nonequilibrium-plasma streamers, leading to immediate formation of five spatially distinct wrinkled flame kernels around each streamer. Compared to the conventional spark ignition, which produces a single flame kernel that exhibits an initial laminar growth regime before wrinkling, corona ignition's early achievement of higher flame surface areas significantly shortened the ignition delay, resulting in reduced overall combustion duration and CCV for each mixture. Additionally, although the lean, dilute mixture produced higher CCV than the stoichiometric, minimally diluted mixture with both igniters, the mixtures ignited by the corona system suffered less than those ignited by the conventional system. Image-based measurements of CCV agreed with those based on in-cylinder pressure.