D. T. Hountalas

Experimental investigation concerning the effect of natural gas percentage on performance and emissions of a DI dual fuel diesel engine

Abstract During the last years a great effort has been made to reduce pollutant emissions from direct injection (DI) diesel engines. Towards this, engineers have proposed various solutions, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines, which use conventional diesel fuel and gaseous fuel, are referred to as dual fuel engines. The main aspiration from the usage of dual fuel (liquid and gaseous one) combustion systems is mainly to reduce particulate emissions and nitrogen oxides. One of the gaseous fuels used is natural gas, which has a relatively high auto ignition temperature and moreover is an economical and clean burning fuel. The high auto ignition temperature of natural gas is a serious advantage against other gaseous fuels since the compression ratio of most conventional DI diesel engines can be maintained. Moreover the combustion of natural gas produces practically no particulates since natural gas contains less dissolved impurities (e.g. sulfur compounds). The present contribution is mainly concerned, with an experimental investigation of the characteristics of dual fuel operation when liquid diesel is partially replaced with natural gas under ambient intake temperature in a DI diesel engine. Results are given revealing the effect of liquid fuel percentage replacement by natural gas on engine performance and emissions.

Operational and Environmental Evaluation of Diesel Engines Burning Oxygen-Enriched Intake Air or Oxygen-Enriched Fuels: A Review

A method to curtail emissions of smoke and other pollutants from diesel engines is to enhance the oxygen supply to their combustion chamber. This can be accomplished by enriching either the intake air stream or the fuel stream with oxygen. Experimental studies concerning the oxygen-enrichment of intake air, have revealed large decrease of ignition delay, drastic decrease of soot emissions as well as reduction of CO and HC emissions while, brake specific fuel consumption (BSFC) remained unaffected and increasing of power output is feasible. However, this technique was accompanied by considerable increase of NO x emissions. Experimental and theoretical studies with oxygenated fuels have demonstrated large decrease of soot emissions, which correlated well with the fuel oxygen content. Reduction of CO and HC emissions with oxygenated fuels was also obtained. However, penalties in both BSFC and NO x emissions have been observed with oxygenation of diesel fuels. In both cases one has to weigh the tradeoffs in fuel economy, in power output and in the emissions of various pollutants. Moreover, fuel cost, availability and supply infrastructure, as well as equipment and operational costs, are among concerns that apply to these techniques. This manuscript presents a comparative evaluation of the two techniques regarding engine performance characteristics, environmental repercussions and economy of operation. The primary objective is to contrast the benefits and the drawbacks of the two techniques in view of economic, operational and environmental parameters. Results have shown that the overall economy of operation of the two techniques may be comparable, if the price of oxygenated fuel blends is similar to that of diesel fuel. Their impact on pollutant emissions may also be comparable, if the oxygen enrichment of either technique is limited to a low level (<23% by mass in the cylinder mixture). However, there are possibilities of increasing the power density of engines with oxygen enrichment of the intake air.

The Effect of Various Dynamic, Thermodynamic and Design Parameters on the Performance of a Turbocharged Diesel Engine Operating under Transient Load Conditions

Thermodynamic, dynamic and design parameters have a significant and often conflicting impact on the transient response of a compression ignition engine. Knowing the contribution of each parameter on transient operation could direct the designer to the appropriate measures for better engine performance. To this aim an explicit simulation program developed is used to study the performance of a turbocharged diesel engine operating under transient load conditions. The simulation developed, based on the filling and emptying approach, provides various innovations as follows: Detailed analysis of thermodynamic and dynamic differential equations, on a degree crank angle basis, accounting for the continuously changing nature of transient operation, analysis of transient mechanical friction, and also a detailed mathematical simulation of the fuel pump. Each equation in the model is solved separately for every cylinder of the 6-cylinder diesel engine considered. The model is validated against experimental data for various load changes. The effect of several dynamic, thermodynamic and design parameters is studied, i.e. load schedule (type, and duration of load applied), turbocharger mass moment of inertia, exhaust manifold volume and configuration, cylinder wall temperature, aftercooler effectiveness as well as an interesting case of a malfunctioning fuel pump. Explicit diagrams are given to show how, after an increase in load, each parameter examined affects the engine speed response, as well as other properties of the engine and turbocharger such as fuel pump rack position, boost pressure and turbocharger speed. It is shown that certain parameters, such as the type of connected loading, the turbocharger inertia, a damaged fuel pump and the exhaust manifold volume, can have a significant effect on the engine and turbocharger transient performance. However others, such as the cylinder wall temperature, the aftercooler effectiveness and the exhaust manifold configuration have a less important effect as regards transient response and final equilibrium conditions.

Prediction of marine diesel engine performance under fault conditions

The diesel engine, due to its superior efficiency when compared to other thermal engines, is widely used for propulsion of marine vessels. Since in such applications the power concentration is critical, most marine diesel engines are of the turbocharged type. Turbocharging has a serious effect on engine performance due to the interaction between the turbocharger and the engine. This interaction makes the detection of engine faults extremely difficult since a specific fault affects the turbocharger and through it the engine. For this reason various methods have been proposed for the detection of engine faults. The present author has in the past presented a method for marine diesel diagnosis by processing measured engine data using a simulation model. In the present work a completely different approach is followed; an attempt is made to use a simulation model to predict marine diesel engine performance under various fault conditions. The method is applied to a newly built vessel powered by a slow speed two stroke marine diesel engine. Using the engine shop trial data obtained under propeller law the simulation model constants are determined, using an automatic method that has been developed. The comparison of results obtained with the data from the official shop trials confirms the accuracy of the model and its ability to predict almost all operating parameters of the engine. The model is then used to produce results by simulating various engine faults or faults of its subsystems. From this analysis their impact on various measurable engine parameters is determined. It is interesting to see that in the case of turbocharged engines some faults have a different effect when compared to naturally aspirated ones. Also, it is revealed that without the use of modeling in many cases it is relatively difficult to determine the actual cause for an engine malfunction, since the observed effects on engine performance are similar. The proposed method is promising and assists the engineer to understand the actual effect of various faults on engine performance. Also it can be used as a training tool since it is easy to simulate various engine faults, a procedure which is extremely difficult, if not impossible, to perform on the field.

A simulation analysis of a DI diesel engine fuel injection system fitted with a constant pressure valve

In the present work, a theoretical and computational investigation is conducted to examine the performance of a fuel injection system fitted with a constant pressure valve, used to power a high speed direct injection (DI) diesel engine. The delivery valve (conventional layout) in the fuel injection system of diesel engines is used to provide a residual pressure in the fuel pipeline for the next injection. However, this layout often results in secondary injections which have a serious effect on engine performance. This problem is more severe in the cases of maintaining high residual pressure values. The use of a secondary valve placed inside the delivery valve, called the constant pressure valve, eliminates this problem by relieving the fuel pipe from the high pressure fluctuations caused by the pressure waves reflected at the injector end and the delivery valve chamber. A relevant experimental investigation is conducted with such a fuel injection system on a high speed direct injection diesel engine, examining the effect of load and speed on the performance of the fuel injection system. The experimental results compare well with the theoretical results obtained from a comprehensive simulation model developed by the present authors. Also, results are presented using the simulation model for the same fuel injection system without being fitted with the constant pressure valve, revealing the occurrence of secondary injections at a high engine speed. The simulation model offers very useful information concerning the design of such a fuel injection system and may be used during the development procedure providing economy in time and a better understanding of the entire injection process.

Development and application of a fully automatic troubleshooting method for large marine diesel engines

The diesel engine is the main propulsion system for marine vessels except for a small category using gas or steam turbines. This is the result of its high efficiency, power concentration and reliability that have been improved considerably during the current decade. Despite these advantages, the engineer usually has to overcome great difficulties and mainly operational problems arising during the engines lifetime. In the case of large marine engines it is almost impossible to apply trial and error methods to solve engine operating problems. This is amplified by the fact that almost all large marine diesel engines are turbocharged ones making the problem even more severe because of the interaction between the engine and the exhaust gas turbocharger. For this reason various diagnosis methods have been proposed for diesel engine condition monitoring that are mainly statistical based on known engine operating curves. These systems provide general information only and do not reveal the actual cause for an engine fault or low performance. In the current work an advanced automatic troubleshooting method based mainly on thermodynamics is presented to monitor the engine condition and to detect the actual cause for an engine fault. The method is based on the processing of measured engine data using a simulation model and provides the current engine condition and its tuning. An application of the method on a marine vessel powered by a slow speed two stroke marine diesel engine suffering from high cylinder exhaust gas temperatures and low power output is given in the present work. The method is applied at sea under actual engine operating conditions. From the processing of measured data the diagnosis method provides the current engine condition and the cause for the low power output from which the engine suffered. After conducting the major repair/adjustments proposed by the diagnosis method a substantial improvement in engine behavior was observed providing a validation for the proposed method.

Experimental and simulation analysis of the transient operation of a turbocharged multi‐cylinder IDI diesel engine

SUMMARY An experimental and theoretical analysis is carried out to study the response of a multi-cylinder, turbocharged, IDI (indirect injection) compression ignition engine, under transient operating conditions. To this aim, a comprehensive digital computer model is developed which solves the governing di⁄erential equations individually for each cylinder, providing thus increased accuracy over previous ‘single-cylinder’ simulations. Special attention has been paid for diversifying the transient operation from the steady-state one, providing improved or even new relations concerning combustion, heat transfer to the cylinder walls, friction, turbocharger and aftercooler operation, and dynamic analysis for the transient case. An extended steady state and transient experimental work is conducted on a specially developed engine test bed configuration, located at the authors’ laboratory, which is connected to a high-speed data acquisition and processing system. The steady-state measurements are used for the calibration of the individual submodel constants. The transient investigation includes both speed and load changes operating schedules. During each transient test four major measurements are continuously made, i.e. engine speed, fuel pump rack position, main chamber pressure and turbocharger compressor boost pressure. The hydraulic brake coupled to the engine possesses a high mass moment of inertia and long nonlinear load-change times, which together with the indirect injection nature of the engine are important challenges for the simulation code. Explicit multiple diagrams are given to describe the engine and turbocharger transient behaviour including smoke predictions. The agreement between experimental and predicted responses is satisfactory, for all the cases examined, proving the validity of the simulation process, while providing useful information for the engine response under various transient operations. ( 1998 John Wiley & Sons, Ltd.

Multi-Zone Combustion Modeling as a Tool for DI Diesel Engine Development – Application for the Effect of Injection Pressure

During the recent years, extensive research conducted worldwide in the field of Heavy Duty Diesel engines has resulted to a significant improvement of engine performance and emissions. These efforts have been assisted from simulation models providing good results. Towards this direction a multi-zone model developed by the authors has been used in the past to examine the effect of injection pressure on Dl diesel engine performance and emissions. The attempt was challenging since no experimental data existed when the calculations were conducted, to support the findings. Eventually, experimental data concerning engine performance and emissions became available using slightly different operating conditions and injection pressure data. In the present study an attempt is made to evaluate the prediction ability of the multi zone model by comparing the theoretical results with experimental data and explain any discrepancies between them. The simulation code used is essentially the same while a calibration has been made only for the soot model, to obtain at one operating point (low injection pressure) similar absolute values. It is promising that the simulation manages to predict for all examined cases the effect of injection pressure on engine performance and emissions. It is confirmed that the increase of injection pressure results to fast combustion and a serious reduction of soot especially at part load and high engine speeds but at the same time to a considerable increase of NO emissions. Predictions from the present study using actual injection rate data and operating conditions are qualitatively similar to the ones of the initial investigation while absolute values are closer to the experimental ones. But since the most important role of modeling is not to capture accurately absolute values but trends, its validity as a prediction tool is revealed.

Experimental Investigation to Specify the Effect of Oxygenated Additive Content and Type on DI Diesel Engine Performance and Emissions

The reduction of brake specific consumption and pollutant emissions are issued as future challenges to diesel engine designers due to the depletion of fossil fuel reserves and to the continuous suppression of emission regulations. These mandates have prompted the automotive industry to couple the development of combustion systems in modern diesel engines with an adequate reformulation of diesel fuels and have stirred interest in the development of clean diesel fuels. The use of oxygenated fuels seems to be a promising solution towards reducing particulate emissions in existing and future diesel motor vehicles. The prospective of minimizing particulate emissions with small fuel consumption penalties seems to be quite attractive in the case of biodiesel fuels, which are considered as an alternative power source. Studies conducted in diffusion flames and compression ignition engines have shown a reduction of soot with increasing oxygen percentage. However, the effects of the type of oxygenated additive and oxygen content on gaseous and particulate emissions obtained from modern DI diesel engines have not been fully investigated. An experimental investigation is conducted to determine the effect of oxygen content and oxygenate type on DI diesel engine performance and emissions. One conventional and three oxygenated fuels are examined having an oxygen content ranging from 0% to 9%. The fuels are prepared by blending a biodiesel compound (RME), Diglyme and Butyl-Diglyme with a low sulfur diesel fuel in various proportions. An experimental installation is prepared and engine tests are conducted on a naturally aspirated single-cylinder Ricardo Hydra research engine. The measurements are carried out at various operating conditions. The experimental findings reveal an increase of in-cylinder pressure due to the increase of cetane number. In addition, a slight increase of bsfc is observed due to the small decrease of fuel heating value with the increase of the oxygen content. A decrease of ignition delay is observed with increasing oxygen content following thus, the increase of cetane number. A considerable reduction of soot, carbon monoxide and unburned hydrocarbon emissions is witnessed while; nitric monoxide emissions are increased when the oxygen content is increased from 3% to 9%. Similar effects are observed when replacing the rapeseed methyl ester with a mixture of diglyme and butyl-diglyme and the oxygen percentage remains unaltered. As revealed, a reduction of tailpipe soot without overall considerable penalties in bsfc and NO x emissions can be achieved in modem DI diesel engines using oxygenated additives at elevated percentages (30% by mass).

Possibilities to Achieve Future Emission Limits for HD DI Diesel Engines Using Internal Measures

The diesel engine is currently the most efficient powertrain for vehicle propulsion. Unfortunately it suffers from rather high particulate and NO x emissions that are directly related to its combustion mechanism. Future emission legislation requires drastic reduction of NO x and particulate matter compared to present values. Engine manufacturers in their effort to meet these limits propose two solutions: reduction of pollutants inside the combustion chamber using internal measures and reduction at the tailpipe using aftertreatment technology. Currently there are various opinions considering the final solution. Taking into account information related to aftertreatment technology, an effort should be made to reduce pollutants inside the combustion chamber as much as possible. The last is obvious if we account for the even more strict emission limits to be applied after 2010 that will require a combination of aftertreatment and internal measures. For this purpose it is examined in the present using a simulation tool the possibility for achieving EURO-V emission limits using conventional Dl diesel engine combustion technology and internal measures only. Towards this aim, the advancement of fuel injection timing and the increase of injection pressure in conjunction with the increase of EGR rate and boost air pressure are considered. These technologies are evaluated comparing performance and emission data against experimental ones referring to the baseline operation of a single cylinder HD Dl diesel test engine. The results are used to examine the potential for meeting EURO-V emission limits using the previous combination of internal measures. The idea is to control soot using internal measures only and use A/T devices to control NO x emissions where necessary. From the results obtained, indication is also provided for the required efficiency of after-treatment systems to fulfill future emission limits. Thus one can decide to use internal measures to control emissions up to a certain point and/or less demanding aftertreatment systems to further fulfill his requirements. Another outcome of the present analysis is the information provided concerning the required increase of boost pressure, which will be demanded by future boost air systems.