Moteur à gaz | EPFL Graph Search

thumb|Moteur à gaz horizontal Otto, de 4 chevaux de force, actionnant dans le domaine d'Ambreville (Eure) 1868 Un moteur à gaz est un moteur à combustion interne utilisant un gaz comme carburant. Histoire Dans son brevet de 1799, Lebon avait prédit que son « gaz hydrogène » (du gaz de bois, dont on peut supposer qu'il contenait au moins 50 % de dihydrogène) serait « une force applicable à toutes espèces de machine ». Le gaz de houille inventé par William Murdoch à la même époque, est nommé « gaz hydrogène carboné » puis gaz d'éclairage (« gas light », voir aussi gaz de ville, et gaz manufacturé) et contient 50 % de dihydrogène, 32 % de méthane, 8 % de monoxyde de carbone. À partir de 1804, François Isaac de Rivaz construit les premiers moteurs à gaz utilisant du gaz de houille. Il s'inspire du fonctionnement du Pistolet de Volta pour construire le premier moteur à combustion interne dont il obtient le brevet le . L'inventeur anglais Samuel Brown (ingénieu

NUMERICAL FLOW SIMULATION OF A NATURAL GAS ENGINE EQUIPPED WITH AN UNSCAVANGED AUTO-IGNITION PRECHAMBER

Daniel Favrat, Stefan Heyne, Jan-Bernhard Vos, Dirk Wunsch

This work is part of ongoing research on stationary natural gas engines equipped with unscavanged prechambers. Spark ignition inside the prechamber has been successfully proven with natural gas as well as biogas, reducing emissions while keeping good efficiencies. The conversion of the prechamber system from spark ignition to auto-ignition will lead to longer maintenance intervals in the case of stationary natural gas engines and to a probable more efficient and cleaner combustion. The latter expectation is based on the combustion mode: HCCI like combustion inside the prechamber and faster combustion in the main chamber due to an earlier arrival of the flame front, compared to prechamber spark ignition. To the authors knowledge no work following this approach has been conducted. From this new approach one of the major difficulties arises. While for standard prechamber systems either the spark plugs or injecting gas directly into the prechamber creating rich conditions guarantee to well know the point of ignition, auto-ignition of a premixed gas does not do so. The basic idea of this prechamber is to create as homogeneous conditions as possible. Then, the reacting mixture streams through the orifices into the main chamber. The difficulty here is to create a state that triggers auto-ignition only inside the prechamber. As temperature is the main influencing factor on the reaction chemistry the prechamber walls are heated, aiming at higher gas temperatures inside the prechamber. However, auto-ignition will take place wherever the energy level is sufficiently elevated. In particular, this causes difficulties in the region of the exhaust valve. In this work the three- dimensional flow conditions in a mono-cylinder test engine were numerically simulated in order to better understand the conditions inside the engine, with the new prechamber configuration. Therefore, a geometric model was created, disregarding intake and exhaust valves to simplify matters. A suitable multi-block mesh for parallel computing was generated and models for the initial and boundary conditions derived. The chemical reactions were incorporated to the flow field, using a 54 species mechanism developed for natural gas combustion by two approaches. In a first step the flow field was superposed with zero-dimensional Chemkin calculations whereas in a second step the species conservation equations were solved together with the Navier Stokes equations, which is much more expensive in calculation time. Finally, the numerical results were compared to experimentally gained data. Results show the sensitivity of the computations to varied initial and boundary conditions and provide a guideline for modifications in order to enhance the prechamber configuration. Numerical results show the risk of auto-ignition in the main chamber. Experimental results could be reproduced numerically in regard to the time dependency of first ignition.

2007

Experimental investigation of prechamber autoignition in a natural gas engine for cogeneration

Daniel Favrat, Stefan Heyne, Michael Meier

A novel ignition concept based on autoignition in an unscavanged prechamber is currently being developed at the Laboratory for Industrial Energy Systems (LENI). On a single cylinder test engine a series of experimental runs (CR=8.5-14, =1-1.6, RPM=1150/1500 min−1) have been realized with natural gas as fuel, comparing the new ignition concept to standard spark ignition. The comparison is based on fuel efficiency and exhaust emissions (CO, THC, NOx). The feasibility of operating the engine in auto-ignition mode has been demonstrated, and the potential of prechamber autoignition, in particular in the lean combustion regime, is indicated by the trends in fuel efficiency and emission concentration. The resistive heating of the prechamber walls has been shown to be an effective mean to trigger ignition. The prechamber could clearly be identified as primary ignition location. A reduction of the cycle-by-cycle variations - due to mixture fluctuations - is necessary to exploit the full potential of this engine concept.

2009

An experimental investigation of a lean burn natural gas prechamber spark ignition engine for cogeneration

Roger Röthlisberger

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5% O2 , respectively), without exhaust gas after treatment. The investigation was carried out on a small size gas engine (6 cylinders, 122 mm bore, 142 mm stroke) and required the development of cooled prechambers and the modification of the engine cylinder heads. The approach was essentially experimental, but included a numerical simulation based on the CFD-code KIVA-3V in order to assist and guide the experimentation. The numerical simulation was carried out in order to evaluate the differences in flow characteristics at the location of the spark plug electrodes between direct and prechamber ignition. Further, the influence of the prechamber geometrical configuration was investigated through variations of the nozzle orifice diameter, number and orientation, as well as prechamber volume and internal shape. Based on the results of the numerical simulation, the most promising prechamber configuration parameters were selected for experimentation. Then, variations of the selected prechamber configuration parameters, as well as of the piston geometry, of the turbocharger characteristics and of the engine operating parameters, were carried out in order to determine their influence on the engine performance and emissions. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. However, this advantage is conditioned by a significant delay of the spark timing in order to generate substantial gas jets. This results in a large decrease in peak cylinder pressure and in an important reduction of NOx, CO and THC emissions. Minimum emissions are achieved at a spark timing of about 8°CABTDC. The prechamber geometrical parametric study indicates that trends which increase the penetration of the gas jets and/or promote an early arrival of the flame front at the piston top land crevice entrance are beneficial to reduce the CO and THC emissions. In comparison with the direct ignition, the prechamber ignition yields approximately 40% and 55% less CO and THC emissions, respectively. However, this also leads to about 2%-point lower fuel conversion efficiency. The optimisation of the turbocharger results in a recovery of about 1%-point in fuel conversion efficiency, but a consequent change in the exhaust manifold gas dynamics causes an increase in THC emissions. At the rated power output (150 kW), the prechamber ignition operation fulfils the Swiss requirements for exhaust gas emissions and still achieves a fuel conversion efficiency higher than 36.5%.