It is quite common practice in automotive and aircraft engine maintenance, operation, and research to employ any one of several types of instruments now on the market for determining the air-fuel ratio by exhaust gas analysis. It was the purpose of this investigation to determine the most important operating characteristics, especially range and accuracy, of each of these types of instruments. The theory underlying the operation of this kind of apparatus was studied critically, and certain tests were performed on representative makes in order to observe the operation of each type under service conditions. These tests consisted essentially of connecting the analyzers to the exhaust pipe of a single-cylinder engine and comparing the analyazer readings with the true air-fuel ratio determined by accurately measuring the air and fuel supplied to the engine while the instruments were being observed. This procedure was repeated for a number of different carburetor settings, all other factors being kept as nearly constant as possible during a given series of runs. The effect of variations in engine spark advance and the pressure of the gas supplied to the instruments was also investigated. The test revealed several interesting facts. Study of the operating principles of the several instruments indicated that they were limited te air fue1 ratios below about 14 to 1, and this has been conclusively proved by these experiments. This limitation applies to thermal conductivity, hot-wire catalytic, and relative density types. W While the most expensive makes of instruments were not tested, it was found that, in general, the limit of accuracy is not greater than one-half of one air-fue1 ratio, regardless of the operating principle employed. Large variations in the pressure and rate of flow of the exhaust supplied to the analyzers were found to cause considerable deviations in those instruments which did not employ some kind of device to insure a steady and uniform supply. Certain features of design and construction which effect the reliability of the various types of exhaust gas analyzers are also reviewed in this thesis, and some of the more important chemical methods of analysis are treated briefly. / Master of Science

This work concerns a systematic study of IC engine operation with 100% biogas as fuel (as opposed to the dual-fuel mode) with particular emphasis on operational issues and the quest for high efficiency strategies. As a first step, a commercially available 1.2 kW genset engine is modified for biogas operation. The conventional premixing of air and biogas is compared with a new manifold injection strategy. The effect of biogas composition on engine performance is also studied. Results from the genset engine study indicate a very low overall efficiency of the system. This is mainly due to the very low compression ratio (4.5) of the engine. To gain further insight into factors that contribute to this low efficiency, thermodynamic engine simulations are conducted. Reasonable agreement with experiments is obtained after incorporating estimated combustion durations. Subsequently, the model is used as a tool to predict effect of different parameters such as compression ratio, spark timing and combustion durations on engine performance and efficiency. Simulations show that significant improvement in performance can be obtained at high compression ratios. As a step towards developing a more efficient system and based on insight obtained from simulations, a high compression ratio (9.2) engine is selected. This engine is coupled to a 3 kW alternator and operated on 100% biogas. Both strategies, i.e., premixing and manifold injection are implemented. The results show very high overall (chemical to electrical) efficiencies with a maximum value of 22% at 1.4 kW with the manifold injection strategy. The new manifold injection strategy proposed here is found to be clearly superior to the conventional premixing method. The main reasons are the higher volumetric efficiency (25% higher than that for the premixing mode of supply) and overall lean operation of the engine across the entire load range. Predictions show excellent agreement with measurements, enabling the model to be used as a tool for further study. Simulations suggest that a higher compression ratio (up to 13) and appropriate spark advance can lead to higher engine power output and efficiency.

In order to meet future emission norms for small carbureted SI engines, such as those used on motorcycles in India, there is a need to study mixture preparation, specifically the two-phase flow exiting the carburetor and entering the inlet manifold. A fully functional, modular experimental rig is designed and erected for performing both qualitative and quantitative flow visualization. The vibrations of the engine are minimized to reduce their effect on the flow. A special, optically accessible tube of square cross-section is added between the carburetor and the inlet manifold, to enable the visualization of flow at the exit of the carburetor. An electronic circuit to obtain a signal for the engine crank angle and convert it to a standard TTL pulse, for use on standard imaging systems to capture cycle resolved-images is also designed. The flow in the optical section is qualitatively visualized using high and low speed cameras. The resulting images and movies show two modes of fuel transport within the inlet manifold, one of which is in the form of a dense cloud of fine fuel droplets during some part of the intake stroke. The second mode is in the form of a film at all times in the cycle, along the lower surface of the inlet manifold during idling and along vertical walls under loaded conditions. Recirculation is seen on the vertical walls of the manifold during idling and under load. Finally, the thickness of the fuel film in the optical section at the exit of the carburetor is measured, using PLIF. This part of the study also reveals that there is a film on upper surface of the optical section, at all loads and speeds. This film is lesser than the resolution of measurement for low loads, and increases to 0.5 mm in the case of highest load and speed attained at full throttle. In contrast to the loaded conditions, during idling, the film occurs on the lower surface of the manifold and its thickness is highest (1 mm.). The film is also present throughout the cycle during idling and all load-speed conditions, suggesting that the mixture that goes into the engine has a significant part of fuel in liquid form.

Prediction of flow and combustion in IC engines remains a challenging task. Traditional Reynolds Averaged Navier Stokes (RANS) methods and emerging Large Eddy Simulation (LES) techniques are being used as reliable mathematical tools for such predictions. However, RANS models have to be further refined to make them more predictive by eliminating or reducing the requirement for application based fine tuning. LES holds a great potential for more accurate predictions in engine related unsteady combustion and associated cycle-tocycle variations. Accordingly, in the present work, new advanced CFD based flow models were developed and validated for RANS and LES modelling of turbulent premixed combustion in SI engines. In the research undertaken for RANS modelling, theoretical and experimental based modifications have been investigated, such that the Bray-Moss-Libby (BML) model can be applied to wall-bounded combustion modelling, eliminating its inherent wall flame acceleration problem. Estimation of integral length scale of turbulence has been made dynamic providing allowances for spatial inhomogeneity of turbulence. A new dynamic formulation has been proposed to evaluate the mean flame wrinkling scale based on the Kolmogorov Pertovsky Piskunow (KPP) analysis and fractal geometry. In addition, a novel empirical correlation to quantify the quenching rates in the influenced zone of the quenching region near solid boundaries has been derived based on experimentally estimated flame image data. Moreover, to model the spark ignition and early stage of flame kernel formation, an improved version of the Discrete Particle Ignition Kernel (DPIK) model was developed, accounting for local bulk flow convection effects. These models were first verified against published benchmark test cases. Subsequently, full cycle combustion in a Ricardo E6 engine for different operating conditions was simulated. An experimental programme was conducted to obtain engine data and operating conditions of the Ricardo E6 engine and the formulated model was validated using the obtained experimental data. Results show that, the present improvements have been successful in eliminating the wall flame acceleration problem, while accurately predicting the in-cylinder pressure rise and flame propagation characteristics throughout the combustion period. In the LES work carried out in this research, the KIVA-4 RANS code was modified to incorporate the LES capability. Various turbulence models were implemented and validated in engine applications. The flame surface density approach was implemented to model the combustion process. A new ignition and flame kernel formation model was also developed to simulate the early stage of flame propagation in the context of LES. A dynamic procedure was formulated, where all model coefficients were locally evaluated using the resolved and test filtered flow properties during the fully turbulent phase of combustion. A test filtering technique was adopted to use in wall bounded systems. The developed methodology was then applied to simulate the combustion and associated unsteady effects in Ricardo E6 spark ignition engine at different operating conditions. Results show that, present LES model has been able to resolve the evolution of a large number of in-cylinder flow structures, which are more influential for engine performance. Predicted heat release rates, flame propagation characteristics, in-cylinder pressure rise and their cyclic variations are also in good agreement with measurements.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

A gasoline direct injection engine was set-up to operate with a dynamometer in a test cell. Test cycle and emissions measurement procedures were developed for evaluating the regulated and non-regulated gaseous emissions. Equipment and techniques for particulate matter measurements were adapted for use with the gasoline direct injection engine. The particulate matter emissions produced by the engine were compared between two different fuels; gasoline and E10 (10% ethanol and 90% gasoline). The gaseous emissions generated by the engine when it was run on gasoline and E30 (30% ethanol and 70% gasoline) were also compared. Particle number decreased with E10 for hot start conditions, while the opposite was observed for cold start conditions. Particulate matter emissions were found to track with acetylene and ethylene emissions.

No description available.

the 18th World Congress The International Federation of Automatic Control, Milano (Italy), August 28 - September 2, 2011

Homogeneously charged spark ignition (SI) engines are unable to stabilise the combustion in ultra lean mixtures, therefore they operate with a near stoichiometric air-fuel ratio (AFR) at all load points. This produces high engine out NOx and CO emissions with a compromise on fuel consumption. Moreover, stoichiometric operation is needed for effective operation of a three way catalyst, which is not adequate to meet future fuel consumption targets. (For complete abstract open document)

Une des solutions pour diminuer les émissions polluantes émises par un moteur à combustion interne est de réinjecter une partie des gaz d’échappement (Exhaust Gas Recirculation, EGR) à l'admission. Cependant, dans le cas d’une dilution du mélange air-carburant trop importante, la combustion est plus instable voire ne pas s’entretenir. L’ajout d’une faible quantité d’hydrogène a le potentiel de contrer cet effet négatif de forte dilution. C’est dans ce contexte que ce travail de thèse est basé sur une étude détaillée des effets combinés de l’ajout de l’hydrogène et de la dilution dans un moteur à allumage commandé alimenté par du méthane ou de l’iso-octane. Dans la première partie de ce travail, le potentiel de l’ajout de l’hydrogène combiné à la dilution, en termes d’émissions polluantes et de rendement global du moteur, est montré. Dans la deuxième partie, afin de mieux comprendre l’effet de l’hydrogène et de la dilution dans un moteur à combustion interne et leurs influences sur les propriétés fondamentales de la combustion, la vitesse de combustion laminaire, paramètre fondamentale, a été déterminée expérimentalement pour des mélanges isooctane ou méthane avec de l’air contenant différents pourcentages d’hydrogène et de dilution. Des corrélations ont pu ainsi être formulées permettant d’estimer la vitesse fondamentale de combustion laminaire pour ces mélanges. Dans la dernière partie, l’utilisation de deux diagnostics optiques (la chemiluminescence de la flamme et la tomographie par plan laser du front de flamme couplé à la mesure de vitesse par vélocimétrie par imagerie de particules) a permis de quantifier l’effet de l’hydrogène et de la dilution sur la propagation de flamme turbulente dans un moteur à allumage commandé muni d’accès optiques. Nous avons ainsi montré que le la vitesse de combustion laminaire a un effet prépondérant, comparé au nombre de Lewis, sur la vitesse de combustion turbulente dans un moteur à allumage commandé. / Optimization of the intake air-fuel mixture composition is one way to reduce pollutant emissions in Spark-Ignition (SI) engines. This can be achieved by operating with a diluted mixture, i.e by recirculating the exhaust. There are however limitations on the level of dilution that can ensure the smooth running of SI engines since diluting the air-fuel mixture induces an increase in combustion duration and in cyclic variations which impair engine performance. Adding an amount of hydrogen to the fuel can extend the dilution and the lean engine operability limits, which is beneficial in reducing both emission levels and fuel consumption. The objective of this study is to investigate the combined effects of hydrogen addition and nitrogen dilution in an SI engine fuelled with iso-octane or methane. In the first part of this study, we proved that high values of indicated engine efficiency and low values of pollutant emissions can be achieved by combining hydrogen addition and diluted air-fuel mixtures in the case of SI engines. In the second part, we provided experimental values of laminar burning velocity for diluted methane or iso-octane/hydrogen/air mixtures for a better understanding of the hydrogen and dilution effects on the fundamental properties of laminar combustion. New correlations to estimate laminar burning speeds of these mixtures were also presented. In the last part, the effects of hydrogen addition, with and without nitrogen dilution, on the turbulent flame propagation were investigated in an optical SI engine fuelled with iso-octane or methane. This study was done by using two different experimental techniques (direct flame radiation visualization and laser tomography images with Particle Image Velocimetry). The main conclusion is that the laminar burning velocity, rather than the Lewis number, has the dominant effect on the turbulent burning velocity in an SI engine.