D.A. Kouremenos

The operation of a turbulence chamber diesel engine with LPG fumigation for exhaust emissions control

An experimental study is conducted to evaluate the use of liquefied petroleum gas (LPG) as a secondary fuel for a Ricardo E-6, naturally aspirated, four-stroke diesel engine having a turbulence combustion chamber (indirect injection). The gaseous LPG is introduced together with the aspirated air (fumigation) at various proportions with respect to the diesel fuel which constitutes the main part. The influence of fuel feed ratios (LPG/diesel), in a vast range of loads, on fuel consumption, pressure diagrams, exhaust smokiness and exhaust gas emissions (nitrogen oxides, hydrocarbons and carbon monoxide) is investigated, the baseline being the single diesel fuel operation. The study for this type of engine, which has not being reported in the literature, shows a promise of the present method and reveals that above 60 per cent of maximum load the whole effect is beneficial concerning specific fuel consumption and smoke reduction. The examination of gaseous pollutant levels shows an involved relation with respect to load and fuel proportions. The best results (coupled to acceptable cylinder pressure levels) is obtained at a diesel fuel substitution value of 75% of maximum load, with an LPG mass fraction in the range 10 to 15%.

Comparative performance and emission studies for vaporized diesel fuel and gasoline as supplements in swirl-chamber diesel engines

An experimental study has been conducted to evaluate and compare the use of fumigated diesel fuel or gasoline as supplementary fuels for a naturally-aspirated, four-stroke diesel engine with a swirl-combustion chamber. The supplementary diesel fuel or gasoline is introduced together with the aspirated air (fumigation) in various proportions with respect to the main diesel fuel, which is injected in the usual manner. The influence of fuel/feed ratios (supplementary or main feed), for a large range of loads, has been examined on fuel consumption, pressure diagrams, exhaust smokiness and exhaustgas emissions (nitrogen oxides, hydrocarbons and carbon monoxide). Knocking limits have been determined. The differences in the measured performance and exhaust-emission parameters from baseline engine operation, when using either supplementary diesel fuel or gasoline fumigated in the intake air, are determined and compared. Our study shows promise for this approach and indicates that above ~60% of maximum load, there is high smoke reduction with only a slight change in specific fuel consumption, when using either one of the supplementary fumigated fuels. Examination of gaseous pollutant levels shows involved relations with respect to load and fuel proportions. Theoretical aspects of the supplementary fuel-mode (fumigation) of combustion are used to explain the observed engine behaviour.

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).

A FORTRAN program for calculating the evaporation rates in diesel engine fuel sprays

Abstract A FORTRAN program based on a theoretical model for predicting the evaporation process of liquid fuel sprays in diesel engines is presented. The injected liquid fuel is assumed to break up into droplets in a high pressure, high temperature environment, just as encountered in a diesel engine cylinder. The complete ‘history’ of the droplets is described by the present program, following their motion as well as the heat absorption and evaporation mechanisms. The theoretical model is based on Newtons Second Law of Motion and the equations expressing the heat and mass balance between droplets and surrounding gas. Accurate correlations are taken into account for the prediction of Sauter Mean Diameter and the thermodynamic and transport properties of fuel.

Use of helium instead of hydrogen in inert gas absorption refrigeration

Abstract The behaviour of helium in place of hydrogen as a pressure equalizing gas in triple-fluid absorption refrigeration units is examined. The main thermodynamic and transport properties of the real NH3/He binary gas mixture are presented in the form of diagrams and analytical expressions, with the temperature and the mass fraction of the mixture as input variables. Among others, the mass or mole fraction of the NH3/He gas mixture as a function of the dry and wet bulb temperatures has been plotted. A computer simulation has been developed to calculate the evaporation of NH3 in a NH3/He atmosphere within an insulated tube, allowing measurement of the composition of the mixture via temperature measurement. The results are compared with the corresponding values of evaporation of NH3 in a NH3/H2 atmosphere.

Prechamber and main chamber insulation effects on the performance of an IDI diesel engine coupled to power turbine

Abstract A thermodynamic simulation of a diesel engine cycle presented in this study which serves the purpose to examine the effects of insulating the main chamber and the prechamber, on the performance characteristics of a naturally aspirated, IDI (indirect injection), diesel engine. The insulation of both combustion chambers is taken into account by the corresponding rise of wall temperature, since this is the final result of insulation useful for the present study. It is found that an improvement of efficiency is achieved when insulating only the prechamber. However, when insulating the main chamber, a serious decrease of engine volumetric efficiency is observed which leads to a decrease of efficiency. The improvement in efficiency rises when a power turbine is incorporated at the engine exhaust, converting (recovering) partially the high energy of exhaust gases to mechanical power, which is transferred to the engine crankshaft via a gearbox (turbocompounding).

A high-efficiency, compound NH3/H2O-H2O/LiBr absorption-refrigeration system

A high-efficiency, compound absorption-refrigeration system is considered, which is composed of two cooperating absorption units using NH3/H2O and H2O/LiBr solutions, respectively. The heat output from the NH3/H2O unit is employed to drive the H2O/LiBr unit. The thermodynamics of the new system are simulated by using a procedure which showed that very high theoretical coefficients of performance may be obtained (up to 230%) compared to the corresponding theoretical values for the usual single absorption units, which do not exceed 100%.

Predicted performance of solar driven H2OLiBr absorption units in Athens

Abstract The hour by hour performance of solar driven H 2 OLiBr absorption units, operating as refrigerators or heat pumps, is predicted during a typical year in the Athens area. The thermodynamic analysis is based on a developed model, which simulates the exact absorption thermodynamic cycle. The hourly values of solar radiation and ambient temperature are estimated from numerical processing of related measurements corresponding to about 20 years. In the case operation as a refrigerator, it has been found that the theoretical coefficient of performance varies during the year from 86 to 96%, and the calculated maximum values of the specific cooling power for January, March, May, July, September and November are 155, 260, 369, 363, 277, and 197 W m −2 per collector, respectively. In the case of operation as a heat pump, the theoretical heat gain factor has been found to be practically constant during the typical year (⋍ 192%) and the calculated maximum values of the specific useful thermal power for the above mentioned months are 264, 504, 825, 890, 658 and 369 W m −2 per collector, respectively.

Measuring the evaporation of NH3 in triple-fluid gas absorption units

Abstract A computer simulation is presented which, among other functions, enables the gas concentrations in NH 3 /H 2 O/H 2 absorption refrigeration units to be determined by suitable temperature measurements. The gas concentration is determined by insulating the evaporator and measuring the inlet and outlet gas temperature, and the wall temperature at the outlet. Because of the pressure influence on the evaporation process, the operating pressure of the unit must also be measured. Numerical results are presented for pressures of 17.5, 20 and 25 bar.