Session: Technical Posters

Paper Number: 120440

120440 - Initial Experimental Results for Lean Natural Gas Combustion in a Pre-Chamber Spark-Ignition Heavy-Duty Multi-Cylinder Engine 

In the United States, natural gas (NG) is primarily used for residential and commercial applications, as well as for electricity generation, but it is also used as an alternative, lower-cost, domestic transportation fuel. NG is of strong interest for medium- and heavy-duty fleets with high annual fuel costs. Diesel fueled engines can operate at lean and highly lean air-to-fuel ratio without requiring a separate ignition system to trigger combustion (compression ignition), while providing a significant thermodynamic advantage. Natural gas has strong resistance to autoignition and requires an ignition system (e.g. spark plug, diesel pilot, laser, etc.).

Conventional spark-based ignition systems have practical limits on allowing natural gas fueled engines to operate extremely lean or dilute, where significant efficiency gains are available. Current spark ignition engines are typically designed for stoichiometric operations and therefore not optimized for lean or high levels of EGR dilution. Lean operation is desired for high efficiency SI engines. However, poor combustion performance sets the upper boundary for efficiency and maximum dilution. Prechamber spark ignition (PCSI) systems have shown the potential to extend the NG-engine lean/dilute combustion limit while maintaining stable operation compared to conventional spark-plug based combustion systems. The PCSI concept has been shown to enable combustion of highly lean mixtures, beyond what is generally achievable in conventional spark ignition engines. A fuel rich pre-chamber combustion event generates radicals which, when discharged into the main chamber, trigger ignition in a distributed fashion within the cylinder, avoiding limitations of traditional flame kernel development.

This work details preliminary results from multi-cylinder engine experiments that have been conducted at Oak Ridge National Laboratory, on a 13L Detroit Diesel engine outfitted with a Mahle Jet Ignition pre-chamber system for all 6 cylinders. A premixed charge of NG and air is inducted into the cylinder during the intake stroke using an added port fuel injection system, while direct injection of NG is performed in the pre-chamber. A parametric study was conducted to understand the effects of pre-chamber volume, nozzle diameter and number, and equivalence ratio, both in the pre-chamber and the main chamber. The overall equivalence ratio was swept from stoichiometric to lean (phi = 0.5) with the objective of finding fundamental relationships between conditions in the pre-chamber and engine performance. With a constant injected fuel energy, the ratio of fueling between pre-chamber and main chamber was varied (injection duration and timing) while controlling air flow through the stock air-handling system. Combustion parameters such as ignition delay, pressure rise rate and engine-out emissions are discussed.

Presenting Author: Scott Curran ORNL

Presenting Author Biography: Dr. Scott Curran leads the Fuel Science and Engine Technologies Research Group at Oak Ridge National Laboratory (ORNL). His research areas include advanced compression ignition experimental research including the development of advanced combustion concepts and investigating the fuel effects on advanced combustion modes. He is involved with low-lifecycle carbon fuels research for transportation and also leads natural gas research and analysis projects. He is also involved in vehicle systems research projects, well-to-wheels analysis for mobile and stationary power sources, the Sustainable ORNL Initiative and is an active collaborator with DOE Clean Cities for alternative fuels and advanced vehicle technology outreach and education and serves on the board of directors for the East Tennessee Clean Fuels Coalition. He served as the vehicle lead for the ORNL Additive Manufacturing Integrated Energy (AMIE) project where ORNL 3D-printed a working range extender vehicle and a small house which share energy. He received his BS and MS in mechanical engineering from the University of Tennessee – Knoxville (UT). He completed his PhD degree in Energy Science and Engineering within the UT/ORNL Bredesen Center.