Knock characteristics of dual-fuel combustion in diesel engines using natural gas as primary fuel

This paper investigates the combustion knock characteristics of diesel engines running on natural gas using pilot injection as means of initiating combustion. The diesel engines knock under normal operating conditions but the knock referred to in this paper is an objectionable one. In the dual-fuel combustion process we have the ignition stage followed by the combustion stage. There are three types of knock: diesel knock, spark knock and knock due to secondary ignition delay of the primary fuel (erratic knock). Several factors have been noted to feature in defining knock characteristics of dual-fuel engines that include ignition delay, pilot quantity, engine load and speed, turbulence and gas flow rate     

Dynamics of electrically charged transient evaporating sprays

The evolution of an evaporating spray plume typical of those under consideration for use in direct injection spark ignition (DISI) engines, for early and late fuel injection strategies is investigated. Here the effect of electric charge, present on individual drops, upon the spray dispersal and evaporation rate is investigated with the aim of optimizing these parameters with respect to typical engine timescales and injection strategy. The predictions suggest that applying electric charge to drops in sprays injected early into the intake stroke does not have a beneficial effect. The spray evaporation rate is not significantly enhanced, and the long time interval between fuel injection and ignition actually promotes spray wall deposition. Conversely, applying electric charge to sprays injected late encourages secondary atomization and the increase in surface area greatly improves the evaporation rate. This is also true at higher engine speeds, corresponding to a much reduced time between fuel injection and ignition. Therefore it is suggested that the selective use of electric charge is viable way of tuning the spray character without effecting fuel metering when moving from an early to a late injection strategy in DISI engines when variable loads are required. Copyright © 2006 John Wiley & Sons, Ltd.     

The sparking plug Some design of considerations

The sparking plug is a good example of the interplay of materials properties and design to give a product of optimum performance. Different engines require different spark plug designs. Methods of “fine-tuning” of the design are discussed for different engine conditions and mention is made of the role of materials changes in the ceramic insulator for economic production and performance.     

Reliability modelling with redundancy—A case study of power generation engines in a wastewater treatment plant

Power generators are critical assets in wastewater treatment plants (WWTPs) in Australia and many countries. Better managing the lifetime, minimising failures, improving reliability and availability, and reducing operating and maintenance costs of the power generation assets are still challenging topics for water utilities. This case study aims to develop power generation system reliability and availability modelling considering redundancy to minimise operation and maintenance costs. The two-parameter Weibull model was used to assess system reliability and availability to power generation engines in WWTPs. The Kaplan-Meier method (a time-driven estimation technique) and the log beta-Weibull model (which is suitable for modelling censored and uncensored data) were used to analyse and validate the modelling results. Shape and scale parameters of the Weibull models were estimated by maximising the log-likelihood function using non-linear optimisation. Hazard and reliability functions were calculated using the Weibull model. Results using two-parameter Weibull, Kaplan-Meier, and log beta-Weibull models display low reliability and high hazard rate over time, which was associated with spark plug failure due to a suboptimal start and stop operation strategy.     

Pulsed charged sprays: application to DISI engines during early injection

Numerical predictions of the temporal evolution of pulsed sprays, typical of those used in gasoline direct injection spark ignition engines are presented, with the novelty that the drops are electrically charged. The rate of spray expansion, in terms of the fraction of maximum possible spray charge for a typical engine timescale, is investigated. The engine timescale chosen is the time available between spray injection and ignition, and for a low‐speed engine operation, with injection during the intake stroke. The aim is to quantify the amount of electric charge, required to spread the spray throughout the engine cylinder, without causing excessive piston and wall impingement, prior to hypothetical ignition. It is found that experimentally realizable amounts of electric charge are sufficient to cause spray expansion throughout the engine cylinder within the timescale permitted. Also noted is a segregation of the smaller drops from their larger cousins, by virtue of the known non‐linear variation in drop charge with drop mass. Since it is known that pulsed fuel injectors producing charged sprays of insulating liquids are a reality then electric charge seems to be a viable route to control and optimize in‐cylinder mixture distribution and hence engine performance, robustness and emissions. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of advanced injection timing on the performance of natural gas in diesel engines

Concern over the environment and/or the increasing demand for conventional fossil fuel has promoted interest in the development of alternative sources of fuel energy for internal combustion (IC) engines. The effect of advanced injection timing on the performance of natural gas used as primary fuel in dual-fuel combustion has been examined. Satisfactory diesel engine combustion demands self-ignition of the fuel as it is injected near the top dead centre (TDC) into the hot swirling compressed cylinder gas. Longer delays between injection and ignition lead to unacceptable rates of pressure rise (diesel knock) because too much fuel is ready to burn when combustion eventually occurs. Natural gas has been noted to exhibit longer ignition delays and slower burning rates especially at low load levels hence resulting in late combustion in the expansion stroke. Advanced injection timing is expected to compensate for these effects. The engine has standard injection timing of 30° before TDC (BTDC). The injection was first advanced by 5.5° given injection timing of 35.5° BTDC. The engine ran for about 5 minutes at this timing and stopped. The engine failed to start upon subsequent attempts. The injection was then advanced by 3.5° (i.e. 33.5° BTDC). The engine ran smoothly on this timing but seemed to incur penalty on fuel consumption especially at high load levels.     

Obtaining a dispersed liquid-gas mixture using a piston machine: Method and possible applications

Experiments confirm the possibility of obtaining a dispersed liquid-gas mixture with the aid of a piston machine. The mixture is formed as a result of the Rayleigh-Taylor instability development and the tur-bulent mixing in a very thin layer of a liquid at the end of a piston moving with deceleration. The possibility of using this phenomenon for (i) obtaining dispersed water-air mixtures for extinguishing fires and (ii) preparing fuel-air mixtures in internal combustion engines is discussed.     

Laser ignition in internal-combustion engines: Sparkless initiation

Laser ignition has been implemented in a single-cylinder internal combustion engine fueled by gasoline. Indicator diagrams (cylinder pressure versus crank angle) were obtained for laser ignition with nano- and microsecond pulses of an Nd:YAG laser. The maximum power of microsecond pulses was below critical for spark initiation, while the radiation wavelength was outside the spectral range of optical absorption by hydrocarbon fuels. Apparently, the ignition starts due to radiation absorption by the oil residues or carbon deposit in the combustion chamber, so that the ability of engine to operate is retained. This initiation of spark-free ignition shows the possibility of using compact semiconductor quantum-cascade lasers operating at wavelengths of about 3.4 μm (for which the optical absorption by fuel mixtures is high) in ignition systems of internal combustion engines.     

柴油/二甲醚混合燃料喷射系统的模拟计算

针对柴油机传统的泵—管—嘴燃油喷射系统,建立了喷射系统的计算模型和柴油/二甲醚混合燃料的密度、体积弹性模量、黏度、表面张力等物性参数公式,同时还进行了不同比例的柴油/二甲醚混合燃料喷射系统的模拟计算.模拟计算结果表明,随着二甲醚掺混比例的增加,针阀开启时间略有延迟,喷油持续期则基本不变,然而喷射压力、喷射速度、累积喷油量均不断减小.     

Numerical Simulation and Calculation of the Process of Interaction between a Swirling Jet and Drift Flow

A mathematical model and results of numerical calculation of the process of interaction between a swirling jet and drift flow are presented in the paper. The structure of flow and the process of chemical reactions are investigated under conditions of transverse injection of a swirling jet of combustion products into a flow of fuel-air mixture. Inferences are made of the possibility of using a transversely injected jet to provide for a gasdynamic stabilization of flame in combustors of gas-turbine engines.     

Interferometric fiber-optic sensor embedded in a spark plug for in-cylinder pressure measurement in engines

Pressure sensing in an internal combustion engine with an intrinsic fiber Fabry-Perot interferometer (FFPI) integrated with a spark plug is demonstrated for the first time. The spark plug was used for the ignition of the cylinder in which it was mounted. The FFPI element, protected with a copper/gold coating, was embedded in a groove in the spark-plug housing. Gas pressure inthe engine induced longitudinal strain in this housing, which was also experienced by the fiber-optic sensing element. The sensor was monitored with a signal conditioning unit containing a chirped distributed-feedback laser. Pressure sensitivities as high as 0.00339 radians round-trip phase shift per pounds per square inch of pressure were observed. Measured pressure versus time traces showed good agreement with those from a piezoelectric reference sensor mounted in the same engine cylinder.     

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NO_x) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NO_x and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.     

玉米淀粉电火花点火数值模拟

在粉尘云电火花点火实验研究的基础上,结合粉尘云点火机理,建立完整的粉尘云点火模型。通过模型计算玉米淀粉的最小点火能,并模拟点火过程中颗粒温度随时间的变化过程,同时分析在无粉尘粒子情况下电火花温度的变化情况。通过模拟计算,得到玉米淀粉在敏感条件下的点火能为2.9 mJ,计算结果与实验数据基本一致,由此可以进一步理解粉尘云的点火过程及电火花放电过程。     

Progressive combustion in SI-Engines—Experimental investigation on influence of combustion related parameters

The fuel heat release rate which virtually controls the combustion process is dependent on the ‘Mass-Fraction-Burnt (MFB)’. In the present research work, a ‘logistic model with conditional variability in MFB’, has been developed for precise simulation of combustion in SI engines as the model has built in routines to take into account such factors as location of spark plug, single/dual spark plugs, intake generated swirl, combustion chamber geometry (associated with Bore/Stroke ratio), etc. A major contribution of this paper is that new and improved models for the ‘overall combustion duration’, and ‘ignition delay/flame development angle’, taking into account primarily the influence of compression ratio on the overall combustion process in SI engine have been developed. Taylor’s original equation for estimating the overall combustion duration has been modified by including a logistic equation for the error term and incorporating it in the original equation. Ignition delay as proposed by Keck et al has been modified by incorporating a polynomial of 3^rd order into the original equation. The empirical correlations that have been proposed in this paper may serve to be the starting point for simulation of ‘photodetonation concept’ to simulate HCCI combustion which is presently the hot research work in the area of pre-mixed combustion. A program in Turbo-C++ has been developed for the complete simulation of SI engine combustion, taking into account the conditional variability effect, variable specific heats of burnt gases, dissociation of gases at high temperatures, progressive combustion phenomena, heat transfer (based onWoschni’s equation), gas exchange process based on 1D-steady gas flow equation employing Taylor’s mach index of 0.6 for valve design.     

Laser-induced fluorescence of ketones at elevated temperatures for pressures up to 20 bars by using a 248 nm excitation laser wavelength: experiments and model improvements

Laser-induced fluorescence of acetone and 3-pentanone for a 248 nm excitation wavelength was investigated for conditions relevant for internal combustion engines regarding temperature, pressure, and gas composition. An optically accessible calibration chamber with continuous gas flow was operated by using CO2 and air as a bath gas. According to the varying pressure and temperature conditions during the compression stroke of a spark ignition engine, fluorescence experiments were performed under isothermal pressure variations from 1 to 20 bars for different temperatures between 293 and 700 K. The ketone fluorescence behavior predictions, based on a model previously developed by Thurber et al. [Appl. Opt. 37, 4963 (1998)], were found to overestimate the pressure-related fluorescence increase for high temperature and small wavelength excitation at 248 nm. The parameters influencing the model only in the large vibrational energy regime were newly adjusted, which resulted in an improved model with a better agreement with the experiment. The model's validity for excitation at larger wavelengths was not influenced. For the air bath gas an additional collision and vibrational energy sensitive quenching rate was implemented in the model for both tracers, acetone and 3-pentanone.     

Experimental investigation of impact of diesel particulate filter on smoke and NO<Subscript>x</Subscript> emissions of a Euro-I compression ignition engine with active and off-board regeneration

Old engines (Euro III or earlier) produce more emissions, and it will be difficult to entirely stop their usage especially in developing and under-developed nations; hence, it is desired that appropriate emission reduction technologies are tested on such engines to analyze their feasibility and economical acceptability. While most such studies have been conducted on constant speed stationary engines and modern engines, this study tried to analyze the effectiveness of an uncoated wall-flow type ceramic diesel particulate filter on a Euro-I, water-cooled, direct injection, variable speed, compression ignition engine in a laboratory set-up in India. Also, this study focused on diesel particulate filter regeneration by two methods: active regeneration by diesel injection in the particulate filter using an electronic control unit and off-board regeneration by taking out and heating the diesel particulate filter in an electrical resistance furnace at 650 °C for 10 h. The results, in the form of smoke emission, NO_x emission and engine performance, obtained using both the regeneration methods were analyzed, and conclusions were drawn. It was found that using diesel particulate filter, particulate matter emissions (smoke) were almost entirely eliminated. It was also found that off-board regeneration had numerous advantages compared to active regeneration. Since a furnace would be needed for off-board regeneration, an exchange process for diesel particulate filter is suggested.     

Modeling of explosion thermal radiation

The hydrodynamic and radiation processes accompanying explosions of chemical explosives and fuel-air mixtures have been considered. Computer modeling of the radiation from a fire ball of explosion and a flame of diffusion combustion of a hydrocarbon fuel has been performed. The dependences of the heat flux density from the region occupied by explosion and combustion products on its temperature and geometric characteristics have been determined. Thermal load distributions on targets of different orientations in the vicinity of the energy release zone have been obtained. A comparison of the thermal parameters on radiation detectors with the criteria of thermal affection of people and ignition of combustible materials has been made.     

汽油机控制参数的电控与测试研究

以MCS－8098单片机作为中央控制器,设计了一种电控发动机基本控制参数测试装置,利用该装置对汽油机的空燃比和点火提前角等控制参数进行了实际测试。应用测试获得的数据对发动机进行实际控制时,取得了比较满意的效果。     

MIKE 3 versus HARTMANN apparatus: comparison of measured minimum ignition energy (MIE)

In this study, MIE values measured with two different explosion tubes, HARTMANN and MIKE 3, are compared. Generally, MIKE 3 apparatus provides MIE results, which are equal or lower to those measured with the HARTMANN apparatus; this is particularly true for the energy ranges between 1 and 10mJ and higher than 100mJ. Differences observed can modify samples classification according to their sensitivity to electrostatic ignition sources. Nevertheless, ignition of a dust cloud by an electrostatic discharge is complex, and implies a different mechanism from that occurring during MIE tests. Thus, it seems difficult to synchronise dust dispersion and spark triggering to obtain optimal concentration in the spark area. Moreover, spark characteristics such as duration or energy feeding rate of spark cannot reproduce exactly industrial-world ones. On this point, it is not possible to conclude if characteristics of MIKE 3 electric circuit, e.g., resistance and inductance, are more relevant than HARTMANN circuit ones.     

Biochemical detection for direct bead surface analysis

A continuous-flow biochemical detection system is presented which recognizes biologically active compounds immobilized to solid phases. This approach can be used to screen, for example, solid-phase combinatorial libraries for lead compounds. Biochemical detection is performed by mixing a plug of a solid-phase suspension with labeled affinity protein. During a short reaction time, the labeled affinity protein will only bind to ligands, i.e., compounds with biological activity. Hereafter, the free and bound labels are separated by means of a hollow fiber module. Quantitation of the free label is performed with a conventional flow-through fluorescence detector. Total assay time amounts to less than 3 min. Biochemical detection for direct bead surface analysis was developed for two model systems. The first model system used fluorescence-labeled avidin as affinity protein and its ligands biotin and iminobiotin immobilized to agarose as analytes. The second model system used fluorescence-labeled antisheep (Fab)(2) fragments as affinity protein and different IgGs immobilized to agarose as analytes. The feasibility of this approach for recognition of solid-phase immobilized ligands was documented by screening 50 samples with a 100% hit rate.