In developing countries like India, a significant automobile market share is held by 2 and 3 wheelers. The small-bore engines used in 2 and 3 wheelers pose unique challenges for attaining low fuel consumption and emissions because solutions should not elevate the cost. These engines use near stoichiometric mixtures. However, lean and ultra-lean combustion will reduce their pumping work, peak combustion temperature, and improve thermal efficiency along with benefits in emissions at part load conditions. Though this can be achieved through direct injection of fuel and stratified charge operation, such methods are too expensive for small engines, and retro-fitment is also difficult. Prechamber/torch chamber ignition systems have been shown to improve lean combustion significantly. Though beneficial in extending lean operation, the application of torch chambers in small engines is very scarce due to the challenges like the need to use tiny pre-chamber volumes and constraints in mounting and orientation of the pre-chamber on the engine and also the spark plug and the injector on the small pre-chamber.
In this work, first simulations were done using a commercial computational fluid dynamics tool to arrive at a suitable torch chamber ignition system configuration for a small 200 cc three-wheeler engine. Initially, the simulation model was validated using experimental data from the same engine under the normal port-fuel-injection with conventional ignition. Using these validation parameters, many simulations were conducted to study the effect and thereby optimise the no of orifices, orifice diameter, location of orifice with respect to pre-chamber axis, and spark location for this small engine configuration.
The designed pre-chamber was fabricated and installed on the cylinder head by enlarging the spark plug hole. And experiments were conducted to evaluate the performance, emissions and combustion using the designed pre-chamber under ultra-lean operation and the results were compared with the same engine operating under the port fuel injection mode and conventional ignition with two different fuels namely gasoline and methanol. Experiments revealed a significant improvement in indicated thermal efficiency especially at part and medium load operation during where the NOx emissions also dropped to insignificant levels. The simulations, experiment results and the comparison will be discussed in detail in this seminar.