Mohand Tazerout

A new indicator for knock detection in gas SI engines

Determination of knock onset for any engine tuning remains a difficult work for many engine manufacturers. This study investigates different combinations of existing knock indices in order to produce an upgraded indicator, which is easier to calibrate. Experiments are conducted on a single-cylinder gas engine bounded to combined heat and power (CHP). Effects of spark advance, volumetric efficiency and equivalent ratio are studied under constant speed operation. The ratio IMPO/(MAPO×W) (with IMPO defined as the Integral of Modulus of Pressure Oscillations, MAPO as the Maximum Amplitude of Pressure Oscillations and W as the width of the computational window) is proposed as suitable indice. In any engine setting, it remains constant under no knocking conditions. When knock occurs, a model deduced from dimensionless analysis allows determination of the oversteps of Knock Limited Spark Advance from a single IMPO/(MAPO×W) measurement with an accuracy better than 1 CA. Knock is then studied for different gas qualities by adding propane or carbon dioxide to the fuel. The results show that there is no significant effect of the fuel composition on the proposed indicator, making the model able to calculate KLSA overstep in all the situations.

The use of biofuel emulsions as fuel for diesel engines: a review

Abstract Animal fats/vegetable oils (called biofuels) and their emulsions are quite promising alternative fuels for diesel engines. This article reports a comprehensive study on the use of animal fats/vegetable oils and their emulsions as fuel in compression ignition engines. Emulsions preparation method and their effects on engine performance, emission, and combustion characteristics have been studied in detail. Information indicates that biofuel emulsions in diesel engines enhanced the combustion efficiency with improved performance as compared to neat fuels. The maximum percentage of water addition to biofuel was found as 30 per cent by volume for maximum efficiency. They reduced NO x , smoke, and particulate emissions considerably. Emulsions resulted in higher ignition delay as a result of vaporization of water as compared to neat fuels. Peak pressure, rate of pressure rise, and premixed combustion rate in the heat release curve were found to be higher when compared to neat oils because of longer ignition delay. Further improvements could be achieved by adding oxygenated fuels like methanol, dimethyl carbonate, and cetane number improvers like diethyl ether with biofuels in small quantities. It has also been suggested that dual fuel operation can significantly reduce particulate and NO x emissions with biofuels. Exhaust gas recirculation can reduce ignition delay considerably with reduced NO x emissions. Finally, modelling techniques were presented because they can help in in-depth analysis of the combustion process of biofuel emulsions in diesel engines.

Thermodynamic analysis of reciprocating compressors

A global model for the thermodynamic analysis of reciprocating compressors is presented. The model is based on five main and four secondary dimensionless physically meaningful parameters. Expressions for the volumetric effectiveness, the work per unit mass and the indicated efficiency are derived. The model has been used in order to predict the performance of a reciprocating air compressor under various operating conditions. The model proves to be a very accurate and useful tool to analyse the compressor performance. The relative importance of the various losses and the influence of different parameters on the reciprocating compressor behaviour are discussed. Especially the in-cylinder residual mass fraction and the walt to fluid heat transfer influences on the reciprocating compressor performance are highlighted

Fuel Savings and CO2 Emissions for Tri-generation Systems

Abstract The paper presents a method for analysing tri-generation systems from the point of view of fuel savings and environmental impact. The authors have focused on the solution of tri-generation plants based on gas turbine or internal combustion engine with an absorption chilling machine. Criteria that characterise the fuel savings and CO2 emissions of tri-generation have been defined. An analysis has been performed for the case of tri-generation with an absorption chilling machine. The mathematical dependence of fuel savings and CO2 emissions on different technical criteria has been analysed. For a certain case there has been plotted the variation of fuel savings as a dependence of technical criteria. The graphs highlight the range of technical criteria with better fuel savings for tri-generation than for separate production. There has been established the order of influence of different technical criteria on fuel savings.

Thermodynamic analysis of tri-generation with absorption chilling machine

The paper presents a method for analysing tri-generation systems. The authors have focused on solutions of tri-generation plants based on gas turbine or internal combustion engine with absorption chilling machine. Several technical criteria have been defined. A thermodynamic analysis has been performed for the case of tri-generation with an absorption chilling machine. From the thermodynamic point of view there have been established the limits for the best energetic performance of tri-generation. The dependence of different technical criteria on each other has also been analysed. A certain case of a tri-generation plant has been analysed using this method. The dependence of the energetic performance of tri-generation on different technical criteria has also been studied.

Knock rating of gaseous fuels in a single cylinder spark ignition engine

Abstract This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative Fuel Research engine). Then, in the second part, the ‘mechanical’ resistance to knock of our engine is highlighted by means of the Methane Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and performances. The error on the SMN and MNR stands beneath ±2 MN units over the gases and engine settings considered.

Optimization of biodiesel production from animal fat residue in wastewater using response surface methodology

Animal fat residues (AFR) from waste water were used as feedstock to produce biodiesel by a two-step acid-catalyzed process. Treatment of the AFRs with 5.4% (w/w) of 17 M H2SO4 at a methanol/AFR ratio of 13:1 (50%w/w) at 60 °C converted more than 95% of the triglycerides into fatty acid methyl esters (FAMEs) with an acid value (AV) of 1.3 mgKOH/gbiodiesel. Response surface methodology indicated that a lower AV cannot be reached using a one-step acid catalyzed process. Thus a two-step acid catalyzed process was employed using 3.6% catalyst and 30% methanol for 5 h for the first step and 1.8% catalyst and 10% methanol for 1 h in the second step, resulting in a yield higher than 98% and an AV of 0.3 mgKOH/gbiodiesel. The product thus conforms to the European norm EN14214 concerning biodiesel.

A Comparative Study of Different Methods of Using Animal Fat as a Fuel in a Compression Ignition Engine

This work explores a comparative study of different methods of using animal fat as afuel in a compression ignition engine. A single-cylinder air-cooled, direct-injection diesel engine is used to test the fuels at 100% and 60% of the maximum engine power output conditions. Initially, animal fat is tested as fuel at normal temperature. Then, it is preheated to 70 degrees C and used as fuel. Finally, animal fat is converted into methanol and ethanol emulsions using water and tested as fuel. A drop in cylinder peak pressure, longer ignition delay, and a lower premixed combustion rate are observed with neat animal fat as compared to neat diesel. With fat preheating and emulsions, there is an improvement in cylinder peak pressure and maximum rate of pressure rise. Ignition delay becomes longer with both the emulsions as compared to neat fats. However preheating shows shorter ignition delay. Improvement in heat release rates is achieved with all the methods as compared to neat fats. At normal temperature, neat animal fat results in higher specific energy consumption and exhaust gas temperature as compared to neat diesel at both power outputs. Preheating and emulsions of animal fat show improvement in performance as compared to neat fat. Smoke is lower with neat fat as compared to neat diesel. It reduces further with all the methods. At peak power output, the smoke level is found as 0.89 m(-1) with methanol, 0.28 m(-1) with ethanol emulsions, and 1.7 m(-1) with fat preheating, whereas it is 3.7 m(-1) with neat fat and 6.3 m(-1) with neat diesel. Methanol and ethanol emulsions significantly reduce NO emissions due to the vaporization of water and alcohols. However NO increases with fat preheating due to high in-cylinder temperature. Higher unburned hydrocarbon and carbon monoxide emissions are found with neat fat as compared to neat diesel at both power outputs. However these emissions are considerably reduced with all the methods. It is finally concluded that adopting emulsification with the animal fat can lead to a reduction in emissions and an improvement in combustion characteristics of a diesel engine.

Determination of the combustion properties of natural gases by pseudo-constituents☆

Abstract This paper presents a methodology for a rapid determination of important natural gas combustion properties (lower heating value, Wobbe index and the stoichiometric air–fuel ratio) using easily detectable physical properties. It is possible to determine natural gas composition by measuring two physical properties and using specific ternary diagrams (CH 4 –C 2 H 6 –C 3 H 8 and CH 4 –C 2 H 6 –N 2 ). The first part of the work deals with the selection of two physical properties from a group comprising thermal conductivity, refraction index, and speed of sound. Then, in the second part, a sensor using the best couple of physical property is used to determine the ternary pseudo-constituents of the gas mixture. The model and the sensor are applied to specific situations such as the online determination of LHV. The error on the combustion properties of natural gas is less than 1% over the gases considered in the present study and over about 20 typical gases supplied over Europe. The effect of small errors in the measurement of physical properties has also been highlighted.

TDC Determination in IC Engines Based on the Thermodynamic Analysis of the Temperature-Entropy Diagram

A thermodynamic methodology of TDC determination in IC engines based on a motoring pressure-time diagram is presented. This method consists in entropy calculation and temperature- entropy diagram analysis. When the TDC position is well calibrated, compression and expansion strokes under motoring conditions are symmetrical with respect to the peak temperature in the (T,S) diagram. Moreover, in case of error on the TDC position, a loop appears which has no thermodynamic significance. Hence an easy methodology has been conceived to obtain the actual position of TDC. This methodology is applied to motoring measurements in order to present its performance, which are compared to usual methods.