Improving the performance of the passive pre-chamber ignition concept for spark-ignition engines fueled with natural gas.

• The passive TJI system fueled by CNG is experimentally and numerically evaluated. • 1D numerical methodology helps to gain knowledge and improve the pre-chamber design. • Experimental results support the findings of the numerical methodology. • Increasing the pre-chamber volume has benefits under restrictive conditions. • An optimum swirl level inside the pre-chamber helps to stabilize combustion. Passive pre-chamber ignition concept has been proven to be an excellent strategy to increase the ignition energy and enhance the combustion velocity even when spark-ignition engines are operating in diluted conditions. Other benefits of this system are the increased combustion stability and combustion efficiency, reducing hydrocarbons and carbon monoxide emissions. However, these advantages are limited at some operation conditions such as low engine load or diluted conditions since both the energy available in the pre-chamber and the scavenge of combustion products are compromised. In this framework, numerical studies using two different computational tools, based on one-dimensional modeling, are utilized to gain knowledge about the governing parameters and to improve the design of a pre-chamber when the engine operates at these restrictive conditions. In particular, the impact of the pre-chamber volume, the total cross sectional area of the holes and tangential angle of the nozzles have been numerically evaluated. Different pre-chamber designs were proposed and experimentally tested in a single-cylinder, high compression ratio turbocharged spark-ignition engine fueled with compressed natural gas and operating on Miller cycle. Results give valuable insight into the key aspects of the internal geometry and some relevant design paths to follow for a suitable pre-chamber definition. [ABSTRACT FROM AUTHOR]