S. Rajkumar

Phenomenological modeling of combustion and emissions for multiple-injection common rail direct injection engines

The high-pressure multiple injections in common rail direct injection diesel engines offer a possibility of simultaneous reduction of exhaust smoke and oxides of nitrogen. The purpose of the present work is to develop a phenomenological model to enable parametric understanding of the combustion and emission characteristics of multiple-injection common rail direct injection engines. The model is based on a two-zone formulation comprising of fuel–air spray and the surrounding air. The model predictions for combustion and emissions are validated with measured results of different multiple-injection schedules available in the published literature. The effect of parametric variations of multiple-injection scheduling on emission characteristics are predicted using the proposed model. It is observed that the simultaneous reduction of oxides of nitrogen and smoke is possible with an optimized pilot fuel quantity and dwell between the injection pulses.

Multi-Zone Phenomenological Model of Combustion and Emission Characteristics and Parametric Investigations for Split Injections and Multiple Injections in Common-Rail Direct-Injection Diesel Engines

This paper presents the formulation of a multi-zone zone phenomenological model for predicting the combustion and emission characteristics of split-injection and multiple-injection common-rail direct-injection diesel engines. In this model, the instantaneous combustion space is divided into two regions, namely the spray zones and the surrounding air. The model predictions for combustion and emissions for split injections and multiple injections are validated with the measured results on a wide range of injection schedules available in the literature. The comparisons reveal the good predictive ability of the model with reasonable accuracy and demonstrate the applicability of the multi-zone model to multiple-injection common-rail direct-injection engines. Hence, the model is used for parametric investigations to analyse the effect of split injections and multiple injections on the combustion and emission characteristics of common-rail direct-injection diesel engines. The parametric investigations show that an increase in the pilot fuel quantity increases the nitrogen oxide emissions and reduces the soot emissions while the dwell period has to be optimized for simultaneous reductions in the nitrogen oxide emissions and the soot emissions. Therefore the present model can be used to achieve an optimal injection schedule for given engine operating conditions.

Effect of Saturation and Unsaturation of Fatty Methyl Esters on Biodiesel NOx Emission Characteristics

Biodiesel is a renewable fuel and an attractive alternative to replace fossil diesel without major engine modifications. However, the emissions of oxides of nitrogen (NOx) from biodiesel fuelled engines are reported to be higher compared to diesel engine. The characteristics of biodiesel are known to depend on their fatty acid methyl ester (FAME) contents which vary with the feedstock. Thus the contribution of saturation and unsaturation of pure components of fatty acid methyl esters on NOx formation warrants a systematic investigation. This paper attempts to relate the composition of biodiesel with NOx formation. For this purpose, the NO formation from pure fatty acid methyl esters are predicted using extended Zeldovich reaction scheme. Also, the experiments are conducted for measuring oxides of nitrogen from a compression ignition engine operated using neat palm and karanja methyl esters and their blends providing biodiesel combinations of varying degree of saturation for investigation. The measured NOx concentrations are compared with the corresponding predictions to affirm the influence of fatty acid methyl ester on engine NOx characteristics. The results clearly indicate that the change in degree of saturation influences the NOx formation and an increase in the degree of saturation of biodiesel decreases the engine NOx emission.

Predicting Mixing Rates in Multiple Injection CRDI Engines

The possibility of multiple-injection in Common Rail Direct Injection (CRDI) engine allows achieving improved combination of oxides of nitrogen (NOx) and smoke emissions. In CRDI engines, the turbulent kinetic energy due to high pressure fuel injection is primarily responsible for fuel air mixing and hence the in-cylinder mixture formation. The air fuel mixing characteristics in the case of multiple-injection are quite different from that of single injection schedule. In this work a zero-dimensional model is proposed for mixing rate calculations with multiple-injection scheduling. The model considers generation and dissipation of in-cylinder turbulence through processes namely fuel injection, air swirl and combustion. The model constants are fine tuned with respect to the data available in existing literature. The model predictions are validated with the available data for the cylinder pressure and heat release rate histories on known single and multiple-injection schedules. These comparisons show good agreement to establish the role of mixing rate variations with multiple-injection. A single set of constants were found to match the cylinder pressure and heat release rate histories for single and multiple-injection from different sources in the literature. Further, the mixing rate and peak temperature predictions of the model are found to relate with the possible effect of specific injection scheduling on emission reductions reported in CRDI engine investigations.© 2009 ASME

Multi-zone phenomenological combustion modeling of biodiesel fueled compression ignition engine

The renewable biodiesel fuel is considered as one of the most promising alternative fuels to compression ignition engines. As there are more than 350 oil-bearing crops with wide variation in their compositional characteristics, it is indispensable to study the combustion characteristics of biodiesel fuels to adopt them as alternative fuels for diesel engines. This article presents a multi-zone phenomenological model for predicting the combustion characteristics of non-edible karanja and jatropha biodiesel fuels in a compression ignition engine. The various thermo-physical properties of the biodiesel fuels needed for the combustion modeling are evaluated based on their methyl ester composition. The model predictions in terms of combustion characteristics of diesel and biodiesel fuels are validated with the experimental results at different engine speed and load conditions. The model predictions are observed to match well with the experimental values within the maximum prediction error of 8.6%. A comparative analysis of combustion characteristics between diesel and biodiesel fuel is also pursued. It is predicted that the peak pressure and spray average peak temperature of karanja and jatropha biodiesel are higher compared to those of diesel fuel which corroborate with the several observations reported in the literature.

Methods for Improving Lift Force of Wind Turbine Aerofoil Blades during Low Wind Speed Conditions – A Review

Wind energy is one of the promising renewable energy resources. The challenges in utilizing the renewable energy sources are making them reliable with good efficiency. Wind turbine plays a major role in industrial power supply during heavy wind conditions. However, in domestic applications, the small scale wind turbine has major issue of low starting torque due to low wind speed near the ground surface. These conditions make the air motion as laminar flow with the Reynolds number less than 5x105. Hence, in some adverse condition there is a laminar flow separation which increases the drag and consequently reduces the lift force. This paper gives a comprehensive review on the investigations that are being carried out on low Reynolds number regime aerofoil and laminar separation bubble to enhance the lift force especially at low wind speed conditions.

CFD Analysis of Heat Transfer Characteristics of Helical Coil Heat Exchangers

The applications of heat exchangers are vast and the enhancement of heat transfer and compact size are the key factors for designing the heat exchangers in order to achieve energy savings. In the field of tubular heat exchangers one of the possible ways for reducing the space occupied by the exchanger is by bending tube axis in helical shape. This option is particularly suitable when construction simplicity is needed and the geometry of the place in which the exchanger has to be housed is the cylindrical one. In this paper, an attempt is made to enhance the heat transfer rate without application of any external power. This is achieved by providing the helical tube in tubes. The parameters influencing the nature of flow in a helical coil heat exchanger are the tube geometry namely pitch coil diameter, pitch and tube diameter. CFD analysis is carried out to study these geometry effects on heat transfer and hydraulic characteristics by varying Reynolds number (hot fluid). The CFD results of velocity and temperature distribution in the heat exchanger are used to estimate the Nusselt number and heat transfer coefficient. This helps to arrive at an optimum value of Reynolds number and Nusselt number for the corresponding tube-to-coil diameter ratios.

Influence of Engine Speed on Mixing and Emission Characteristics of Multiple-Injection Common Rail Direct Injection Diesel Engine

Increase in engine speed increases the in-cylinder turbulence and hence the rate of mixing. However, it is difficult to directly measure the mixing rate and relating its effect on emissions. Hence, in this paper, the comparison of mixing rate at different engine speeds are demonstrated with a multi-zone phenomenological model which has been developed and validated on a wide range of engine operating conditions. The mixing rate is evaluated using a standard quasi-dimensional k-ε formulation. The quantitative predictions of mixing rates at different engine speed substantiate the cause of soot emission reduction at higher engine speed.

Zero-Dimensional Analysis of Combustion in a Multiple-Injection CRDI Engine Using Wiebe Law

Common rail direct injection system (CRDI) offers the potential to achieve optimal combustion and emission characteristics. An empirical analysis of engine combustion process incorporating Wiebe type burn rate law approach is useful not only in understanding the combustion characteristics of a CRDI engine but also aids in diagnosis and control of the combustion process wherever required from the performance and emission standpoint. This paper presents a methodology for applying the burn rate law for common rail direct injection diesel engines adopted with split injection by using Wiebe’s correlation. The analysis reveals that while the empirical constant ‘m’ (shape factor) for both pilot and main injections is independent of engine load and seems to be affected by engine speed only, the constant ‘a’ (efficiency parameter) seems to be influenced by the engine speed, load and injection conditions. A correlation for these empirical constants with the respective parameters of dependence can be formulated which can be used to analyze the effect of change in engine operating conditions on combustion characteristics without conducting engine experiments.

Modeling the Spray Characteristics of Biodiesel

Biodiesel is considered as one most of the promising alternate fuels for the diesel engines without any major engine modifications due to its similar properties that of diesel. However, it is imperative to study the fuel spray behavior and its effective distribution inside the engine which affect combustion and emission characteristics. Hence, a model will be a useful tool in analyzing the spray characteristics of different biodiesel fuels. Therefore, in this paper a numerical modeling is pursued to analyse the spray characteristics namely spray penetration, spray angle, and atomization of biodiesel. This model is likely to be useful for biodiesel combustion modeling.