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Giakoumis E.G.,Internal Combustion Engines Laboratory
Energy | Year: 2010

The modeling of transient turbocharged diesel engine operation appeared in the early seventies and continues to be in the focal point of research, due to the importance of transient response in the everyday operating conditions of engines. The majority of research has focused so far on issues concerning thermodynamic modeling, as these directly affect performance and pollutants' emissions. On the other hand, issues concerning the dynamics of transient operation are usually over-simplified, possibly for the sake of speeding up program execution time. In the present work, an experimentally validated transient diesel engine simulation code is used to study and evaluate the importance of the lubricating oil properties (oil-type, viscosity, temperature) on the transient response of a turbocharged diesel engine. It is revealed how the lubricating oil affects mechanical friction and hence, the speed response as well as the other interesting parameters, e.g. fuel pump rack position or turbocharger operating point for load-change schedules typical in the European Transient Cycles for heavy-duty engines. Particularly under low ambient conditions, the high oil viscosity is responsible for a significant increase in the respective frictional losses worsening the engine transient response. © 2009 Elsevier Ltd. All rights reserved. Source


Papagiannakis R.G.,Hellenic Air Force Academy | Rakopoulos C.D.,Internal Combustion Engines Laboratory | Hountalas D.T.,Internal Combustion Engines Laboratory | Rakopoulos D.C.,Internal Combustion Engines Laboratory
Fuel | Year: 2010

In the effort to reduce pollutant emissions from diesel engines various solutions have been proposed, one of which is the use of natural gas as supplement to liquid diesel fuel, with these engines referred to as fumigated, dual fuel, compression ignition engines. One of the main purposes of using natural gas in dual fuel (liquid and gaseous one) combustion systems is to reduce particulate emissions and nitrogen oxides. Natural gas is a clean burning fuel; it possesses a relatively high auto-ignition temperature, which is a serious advantage over other gaseous fuels since then the compression ratio of most conventional direct injection (DI) diesel engines can be maintained high. In the present work, an experimental investigation has been conducted to examine the effects of the total air-fuel ratio on the efficiency and pollutant emissions of a high speed, compression ignition engine located at the authors' laboratory, where liquid diesel fuel is partially substituted by natural gas in various proportions, with the natural gas fumigated into the intake air. The experimental results disclose the effect of these parameters on brake thermal efficiency, exhaust gas temperature, nitric oxide, carbon monoxide, unburned hydrocarbons and soot emissions, with the beneficial effect of the presence of natural gas being revealed. Given that the experimental measurements cover a wide range of liquid diesel supplementary ratios without any appearance of knocking phenomena, the belief is strengthened that the findings of the present work can be very valuable if opted to apply this technology on existing DI diesel engines. © 2009 Elsevier Ltd. All rights reserved. Source


Lamaris V.T.,Internal Combustion Engines Laboratory | Hountalas D.T.,Internal Combustion Engines Laboratory
Energy Conversion and Management | Year: 2010

Diesel engines are widely used in marine applications (i.e. propulsion and auxiliaries) except from a few cases where gas or steam turbines are used. This is the result of their high efficiency, power concentration and reliability compared to other compatible or alternative power sources. The proper and efficient operation of the engines (main engine and diesel generator units) in marine applications is critical, and therefore techniques or systems that determine engine current condition and detect potential faults are extremely important. Furthermore, it is advantageous when such techniques can be applied on different engine configurations and provide reliable results, because on a vessel usually exist diesel engines of different type, i.e. the main propulsion unit is a large low-speed two-stroke diesel engine while the diesel generators are four-stroke medium or high speed engines. In the present work is described and evaluated for the first time the application of an improved diagnostic technique, developed by the authors, on both the main engine and the auxiliary units of a commercial marine vessel. The diagnostic technique is based on a thermodynamic simulation model. The simulation model embedded in the technique has been modified, namely an existing two-zone model is replaced by a multi-zone one. With this modification it is avoided model constant tuning with the operating conditions. This is extremely important for the diagnostic philosophy of the proposed technique. Using data from engine shop tests, the simulation model is calibrated (i.e. model constants are determined) and the engine reference condition is obtained. The simulation model is then used to estimate the current engine condition, using field measurements (i.e. cylinder pressure measurements, periphery data, etc.). From the results it is revealed that the diagnosis method provides detailed information for the operating condition of both engines and the values of parameters that cannot be measured on the field. To further evaluate the diagnostic procedure, results of the diagnosis analysis are compared with respective readings from existing instrumentation (i.e. brake power output, etc.), showing good agreement. From the investigation it is shown that the diagnostic technique can be applied on both engine types without modifications providing a useful integrated solution for the entire vessel power plant. This is extremely important because conventional systems are usually suitable only for the main engine even though auxiliary units are of significant importance. © 2009 Elsevier Ltd. All rights reserved. Source


Rakopoulos C.D.,Internal Combustion Engines Laboratory | Kosmadakis G.M.,Internal Combustion Engines Laboratory | Pariotis E.G.,Hellenic Naval Academy
Applied Energy | Year: 2010

The scope of the present study is to try to determine a comprehensive heat transfer formulation, which would be able to predict adequately the heat transfer mechanism on a wide range of different reciprocating engine configurations (spark-ignition and diesel engines) and operating conditions. To this aim, four of the most popular heat transfer formulations used in commercial and research CFD (computational fluid dynamics) codes are evaluated comparatively against available experimental data, using an in-house CFD model that has already been applied satisfactorily for the simulation of a spark-ignition and a diesel engine running under motoring conditions. The comparison reveals that most of the existing wall heat transfer formulations fail to predict adequately both the history and peak value of the heat flux. Nonetheless, the predicted trends of the heat flux during the entire closed part of the engine cycle are similar, with higher differences occurring during the expansion phase. To overcome this, the present authors proceeded to the development of a new wall heat transfer formulation based on the existing ones. This new formulation is used in the in-house CFD model for the simulation of the heat transfer through the cylinder walls for the same engines and operating conditions as those used for the comparative evaluation of the existing heat transfer models. Comparing the calculated heat flux using the five heat transfer models with the corresponding measured one, it is concluded that in most cases the new model predicts more accurately the heat transfer during the compression stroke for motored operation and at the same time the predicted peak heat flux is closer to the experimental one. Although a more fundamental formulation is used to describe the heat transfer process, the computational time required is not affected, which is a parameter crucial for multi-dimensional modeling. © 2009 Elsevier Ltd. All rights reserved. Source


Giakoumis E.G.,Internal Combustion Engines Laboratory | Alafouzos A.I.,Internal Combustion Engines Laboratory
Applied Energy | Year: 2010

An engine mapping-based methodology was developed in order to be able to make a first approximation of the engine performance and emissions during a speed/torque vs. time Transient Cycle. The procedure is based on a previous steady-state experimental investigation of the engine for the formulation of polynomial expressions of all interesting engine properties with respect to engine speed and torque. Correction coefficients are then applied to account for transient discrepancies based on individual transient experiments. The developed algorithm was applied for the case of a heavy-duty diesel engine running on the European Transient Cycle. A comparative analysis was performed for each section of the Cycle, which revealed that the first part (urban driving) is responsible for the biggest amount of emissions (in g) owing to the most frequent and abrupt load changes involved. The obvious advantage of the proposed methodology is the fact that the effect of internal or external (after-treatment) measures can be easily incorporated in the code and quantified in terms of emissions improvement. © 2009 Elsevier Ltd. All rights reserved. Source

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