Papers by Theodoros Zannis
Abstract Diesel engine manufacturers have succeeded in developing engines with high power concent... more Abstract Diesel engine manufacturers have succeeded in developing engines with high power concentration and thermal efficiency without disregarding to comply with the continuous stringent emission regulations. Nowadays, several techniques such as ...
Bookmarks Related papers MentionsView impact
Sae International Journal of Fuels and Lubricants, 2004
Résumé/Abstract A method to curtail emissions of smoke and other pollutants from diesel engines i... more Résumé/Abstract 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. ...
Bookmarks Related papers MentionsView impact
ABSTRACT A theoretical study is conducted herein using a newly developed simulation model to exam... more ABSTRACT A theoretical study is conducted herein using a newly developed simulation model to examine the potentiality of improving the overall efficiency of a heavy-duty truck diesel engine with an organic Rankine bottoming cycle by recovering heat from the exhaust gase. For this reason a thermodynamic simulation model of the Rankine cycle has been developed to calculate the performance parameters of the bottoming cycle. The proposed Rankine cycle simulation considers for the impact of pressure drop in the exhaust gas heat exchanger on engine back-pressure. Volume and weight constraints of the exhaust gas heat exchanger are also considered for in the thermodynamic model. A parametric study is performed using the developed model to examine the effects of various organic Rankine cycle parameters on the thermal performance characteristics of the Diesel-Rankine installation. Predictions are given for several operational parameters of the heat recovery installation such as the relative bsfc improvement, the cycle generated power and the organic vapour temperature and mass flow at the various engine loads considered. Predictions are compared with pertinent results derived for a similar diesel truck Rankine cycle operating with water. The analysis of this comparative evaluation reveals that higher values of Diesel – Rankine total efficiency may be attained for the entire operating range of diesel engine when organic medium is used instead of water vapour.
Bookmarks Related papers MentionsView impact
Abstract Engineers use phenomenological simulation models to determine engine performance. Using ... more Abstract Engineers use phenomenological simulation models to determine engine performance. Using these models, we can predict with reasonable accuracy the heat release rate mechanism inside the engine cylinder, which enables us to obtain a ...
Bookmarks Related papers MentionsView impact
ASME 2009 Internal Combustion Engine Division Fall Technical Conference, 2009
ABSTRACT Increasing the in-cylinder oxygen availability of diesel engines is an effective method ... more ABSTRACT Increasing the in-cylinder oxygen availability of diesel engines is an effective method to improve combustion efficiency and to reduce particulate emissions. Past work on oxygen-enrichment of the intake air, revealed a large decrease of ignition delay, a remarkable decrease of soot emissions as well as reduction of CO and unburned hydrocarbon (HC) emissions while, brake specific fuel consumption (bsfc) remained unaffected or even improved. Moreover, experiments conducted in the past by authors revealed that oxygen-enrichment of the intake air (from 21% to 25% oxygen mole fraction) under high fuelling rates resulted to an increase of brake power output by 10%. However, a considerable increase of NOx emissions was recorded. This manuscript, presents the results of a theoretical investigation that examines the effect of oxygen enrichment of intake air, up to 30%v/v, on the local combustion characteristics, soot and NO concentrations under the following two in-cylinder mixing conditions: (1) lean in-cylinder average fuel/oxygen equivalence ratio (constant fuelling rate) and (2) constant in-cylinder average fuel/oxygen equivalence ratio (increased fuelling rate). A phenomenological engine simulation model is used to shed light into the influence of the oxygen content of combustion air on the distribution of combustion parameters, soot and nitric oxide inside the fuel jet, in all cases considered. Simulations were made for a naturally aspirated single-cylinder DI diesel engine “Lister LV1” at 2500 rpm and at various engine loads. The outcome of this theoretical investigation was contrasted with published experimental findings.
Bookmarks Related papers MentionsView impact
Volume 3: Combustion Science and Engineering, 2009
ABSTRACT The simultaneous reduction of nitrogen oxide emissions and particulate matter in a compr... more ABSTRACT The simultaneous reduction of nitrogen oxide emissions and particulate matter in a compression ignition environment is quite difficult due to the soot/NOx trade off and it is often accompanied by fuel consumption penalties. Thus, fuel reformulation is also essential for the curtailment of diesel pollutant emissions along with the optimization of combustion-related design factors and exhaust after-treatment equipment. Various solutions have been proposed for improving the combustion process of conventional diesel engines and reducing the exhaust emissions without making serious modifications on the engine, one of which is the use of natural gas as a supplement for the conventional diesel fuel (Dual Fuel Natural Gas/Diesel Engines). Natural gas is considered to be quite promising since its cost is relative lower compared to conventional fuels and it has high auto-ignition temperature compared to other gaseous fuels facilitating thus its use on future and existing fleet of small high speed direct injection diesel engines without serious modifications on their structure. Moreover, natural gas does not generate particulates when burned in engines. The most common natural gas/diesel operating mode is referred to as the Pilot Ignited Natural Gas Diesel Engine (P.I.N.G.D.E). Here, the primary fuel is natural gas that controls the engine power output, while the pilot diesel fuel injected near the end of the compression stroke autoignites and creates ignition sources for the surrounding gaseous fuel mixture to be burned. Previous research studies have shown that the main disadvantage of this dual fuel combustion is its negative impact on engine efficiency compared to the normal diesel operation, while carbon monoxide emissions are also increased. The specific engine operating mode, in comparison with conventional diesel fuel operation, suffers from low brake engine efficiency and high carbon monoxide (CO) emissions. The influence becomes more evident at part load conditions. Intake charge temperature, pilot fuel quantity and injection advance are some of the engine parameters which influence significantly the combustion mechanism inside the combustion chamber of a Pilot Ignited Natural Gas Diesel Engine. In order to be examined the effect of these parameters on performance and exhaust emissions of a natural gas/diesel engine a theoretical investigation has been conducted by using a numerical simulation. In order to be examined the effect of increased air inlet temperature combined with increased pilot fuel quantity and its injection timing on performance and exhaust emissions of a pilot ignited natural gas-diesel engine, a theoretical investigation has been conducted by using a comprehensive two-zone phenomenological model. The results concerning engine performance characteristics and NO, CO and Soot emissions for various engine operating conditions (i.e. load and engine speed), comes from the employment of a comprehensive two-zone phenomenological model which had been applied on a high-speed natural gas/diesel engine. The main objectives of this comparative assessment are to record and to comparatively evaluate the relative impact each one of the above mentioned parameters on engine performance characteristics and emitted pollutants. Furthermore, the present investigation deals with the determining of optimum combinations between the parameters referred before since at high engine load conditions, the simultaneous increase some of the specific parameters may lead in undesirable results about engine performance characteristics. The conclusions of the specific investigation will be extremely valuable for the application of this technology on existing DI diesel engines.
Bookmarks Related papers MentionsView impact
Volume 3: Combustion Science and Engineering, 2008
ABSTRACT A multi-zone combustion model is used in the present study to examine the effect of incr... more ABSTRACT A multi-zone combustion model is used in the present study to examine the effect of increased in-cylinder oxygen availability (either by using oxygenated fuels or by increasing the oxygen percentage of intake air) on direct injection (DI) diesel engine performance characteristics and pollutant emissions. Simulations are produced for a single-cylinder DI diesel engine (“Lister LV1”) by keeping constant the oxygen content of in-cylinder fuel/air mixture and the engine brake torque. The effects of the two oxygen-enhancement techniques on combustion characteristics, soot and NO concentrations inside the combustion chamber are examined using model predictions for a common diesel oil, a neat oxygenate and the case of increasing the oxygen fraction of intake air. The multi-zone model is also utilized to interpret the relative impact of fuel-side and air-side oxygen on soot formation mechanism by examining the temporal evolution of combustion characteristics and soot formation and oxidation rates inside the fuel jet zones. Evaluation of the theoretical results revealed that the increase of in-cylinder oxygen availability by both techniques resulted in earlier initiation of combustion, increase of peak cylinder pressure and increase of in-cylinder and exhaust NO concentrations. It resulted also in reduction of exhaust gas temperature and exhaust soot values. Fuel oxygen addition was proven to be more influential on combustion process and consequently, on soot and NO formation mechanism compared to oxygen-enhancement of intake air. This is attributed to the higher oxygen availability inside each fuel jet zone, which is observed in the case of oxygenated fuel combustion.
Bookmarks Related papers MentionsView impact
Journal of the Energy Institute
Résumé/Abstract An experimental investigation is conducted to examine the effect of fuel aromatic... more Résumé/Abstract An experimental investigation is conducted to examine the effect of fuel aromatic fraction and type on DI diesel engine performance, gaseous and particulate emissions. Various diesel fuels with total aromatics between 0 and 27% were tested in a ...
Bookmarks Related papers MentionsView impact
In the present study a thermodynamic model was devel-oped and it was used to assess the first-law... more In the present study a thermodynamic model was devel-oped and it was used to assess the first-law and the second-law performance characteristics of a four-stroke marine diesel engine equipped with a regenerative organic Rankine cycle (RORC) bottoming system. Initially, the first and the second law of thermodynamics were utilized to comparatively evaluate the performance characteristics of a diesel-RORC and a diesel-ORC bottoming systems using the same dry organic fluid (i.e. R245ca) and under the same cycle high pressure (i.e. 8 bar). Afterwards, the effect of bottoming cycle high pressure on the marine diesel-RORC system first and second law performance parameters was investigated considering the same dry organic medium (i.e. R245ca). Finally, the theoretical analysis was concluded by examining the effect of dry organic fluid on marine diesel-RORC energetic and exergetic performance characteristics. This investigation was facilitated considering four different dry organic fluids na...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
As recognized by various researchers the most important source of information for a reciprocating... more As recognized by various researchers the most important source of information for a reciprocating internal combustion engine is the cylinder pressure diagram. Its validity for direct injection (DI) diesel engines is extremely important since the engineer can estimate and understand the effect of various operating or design parameters on the combustion mechanism. But, since the measured cylinder pressure diagram is the result of various thermo-physical processes taking place inside the combustion chamber it cannot provide direct information concerning the combustion rate of fuel. For this reason techniques have been developed to estimate the rate at which energy is released inside the combustion chamber by processing the cylinder pressure diagram. These techniques are referred to as “Heat Release Rate Analysis” and are used to estimate the combustion rate of fuel inside the combustion chamber. During its estimation various errors may arise due to either the cylinder pressure measurem...
Bookmarks Related papers MentionsView impact
SAE International Journal of Engines
http://saeeng.saejournals.org/content/5/4/1693.abstract
Bookmarks Related papers MentionsView impact
In the present study, an existing multi-zone combustion model has been modified and applied to pr... more In the present study, an existing multi-zone combustion model has been modified and applied to predict the performance characteristics and the NOx emissions of a large-scale two-stroke diesel engine (i.e. 12.5 MW rated power). Initially, an attempt was made to examine whether the multi-zone model can predict with sufficient accuracy the main performance parameters of the stationary diesel engine, using input data from the shop tests (i.e. engine speed, fuel consumption and scavenging pressure at different engine loads). Hence, it was verified that the model is capable of describing the main performance characteristics of the engine with satisfactory accuracy (i.e. reference state). Further on, an experimental investigation was conducted on the specific engine, consisting of a series of performance and NOx emissions measurements that were conducted at constant speed and at three different engine loads. Then, the proposed model was applied at the present engine condition to evaluate i...
Bookmarks Related papers MentionsView impact
The operation of large, spark ignited piston engines fuelled by natural gas, which are commonly u... more The operation of large, spark ignited piston engines fuelled by natural gas, which are commonly used to generate electricity, contribute significantly to increasing the concentration of nitrogen oxides (NO) in the atmosphere, especially in densely populated areas. Due to its serious environmental impact, the reduction in NO has become a major focus in the fight against air pollution. To resolve this problem various solutions have been proposed, one of them is the nitrogen-enrichment of the inducted air (NEIA). Introduction of inert diluents, such as nitrogen, into a fuel-air mixture slow down the combustion temperature. Low temperature combustion is one of the pathways to meet the mandatory ultra low NO emissions levels. In order to be examined the effect of nitrogen-enrichment of the inducted air on performance and exhaust emissions of a large, spark-ignited, engine fuelled with natural gas, a theoretical investigation has been conducted by using a comprehensive two-zone phenomenol...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
A considerable amount of fuel chemical energy supplied to diesel engines is rejected to the envir... more A considerable amount of fuel chemical energy supplied to diesel engines is rejected to the environment through exhaust gases. It is approximately 30-40% of the energy supplied by the fuel depending on engine load. Therefore if part of this energy is recovered, it could result to significant reduction of engine bsfc compared to other technological solutions. A promising solution for the utilization of exhaust heat is turbocompounding, which has various advantages compared to other techniques as far as packaging, cost and applicability of the system is concerned. The idea is not new because various attempts have been reported but with marginal fuel savings. However, there exists a potential for significant improvement of fuel saving especially when the system is applied on engines with reduced heat losses. For this reason, in the present work, a detailed investigation is conducted to investigate and compare the effect of mechanical and electrical turbocompounding technologies on engi...
Bookmarks Related papers MentionsView impact
Journal of Energy Engineering
The gasification of wood allows the production of wood-gas, which can be used as energy source in... more The gasification of wood allows the production of wood-gas, which can be used as energy source in large spark-ignition (SI) piston engines located in agricultural areas for generating electric power. The composition of wood-gas depends upon the fuel source and the processing technique. The primary objective of the present work is to investigate the main performance and emission characteristics of a multi-cylinder, four-stroke, turbocharged, spark-ignited engine fueled with three different types of wood-gas, at various air to fuel excess ratios. This engine is used for electricity production especially in small generator sets. In order to examine the effect of wood-gas composition on performance and exhaust emissions, a theoretical investigation is conducted by using a comprehensive two-zone phenomenological model. The results concern some of the main engine performance characteristics, i.e. brake specific fuel consumption and maximum cylinder pressure, and specific NO and CO emissio...
Bookmarks Related papers MentionsView impact
Applied Thermal Engineering
A thermodynamic model was developed and used to assess the sensitivity of thermal performance cha... more A thermodynamic model was developed and used to assess the sensitivity of thermal performance characteristics of a closed wet cooling tower to inlet air conditions. In the present study, three cases of different ambient conditions are considered: In the first case, the average mid-winter and mid-summer conditions as well as the extreme case of high temperature and relative humidity, in Athens (Greece) during summer are considered according to the Greek Regulation for Buildings Energy Performance. In the second case, the varied inlet air relative humidity while the inlet air dry bulb temperature remains constant were taken into account. In the last case, the effects on cooling tower thermal behaviour when the inlet air wet bulb temperature remains constant were examined. The proposed model is capable of predicting the variation of air thermodynamic properties, sprayed water and serpentine water temperature inside the closed wet cooling tower along its height. The reliability of simul...
Bookmarks Related papers MentionsView impact
Uploads
Papers by Theodoros Zannis