Study on the ignitability of a high-pressure direct-injected methane jet using a scavenged pre-chamber under a wide range of conditions

Abstract

Natural gas is a promising alternative fuel for internal combustion engines, it allows for a reduction of engine-out emissions without impairing high engine efficiencies. Although this approach is already utilized from small to large engine classes, it is almost exclusively based on the combustion of a premixed homogeneous charge. For ignition, small engines use standard spark plugs or pre-chambers, while large and lean-operated engines use pre-chambers and pilot injections. Direct high-pressure gas injection is a more recent, alternative way to operate gas engines which offers benefits compared to premixed operation such as high combustion pressures, leaner operation, easier quantity regulation, and higher compression ratios, among others. However, in contrast to diesel injection, the compression temperatures are too low for the auto-ignition of the gas jets. Therefore, an additional ignition system is required, usually a pilot injection system is used. In this study, the usability and performance of a scavenged pre-chamber used for the ignition a high-pressure gas jet has been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. Results show that the turbulent hot jet generated by the pre-chamber was able to ignite the high-pressure gas jet under a wide range of operating conditions. Moreover, it also appears to be a promising ignition strategy for very early direct injection during the compression stroke as well as for port injection. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

Experimental study of lube oil pre-ignition in an optical gas engine test rig

“…22 The adaptable setup with flexible operation modes has been used extensively for dual-fuel combustion process investigations with methane as the main fuel. 17,18 With its optically accessible cylinder head, pre-ignition phenomena in dual-fuel operation can be observed very well under engine-relevant conditions and the fundamentals can be investigated. The flexible test rig can be operated in many different combustion modes such as diffusive, homogeneous, or dual-fuel mode (RCCI) as stated in Humair et al 23 Figure 4 shows the working principle of the Flex-OeCoS test rig: One cylinder of a motor-driven engine block feeds a mixture charge into an optical combustion chamber (Ø 60 mm × 20 mm), providing maximum optical access through rectangular and round sapphire windows at each side.…”

“…To study the pre-ignition of lube oil, a series of measurements related to pre-ignition onset will be performed with no additional ignition sources. [17][18][19][20] In particular, the determination of the inflammation phase as well as the flame kernel growth is of interest. Moreover, implications on the subsequent combustion phase and flame propagation will be acquired.…”

“…Furthermore, it offers excellent optical access for the application of different optical measurement methods to acquire pre-ignition inflammation and flame kernel growth. 17,18 Optical access to the whole combustion chamber during the injection of lube oil and/or the presence of a hotspot inside the cylinder provides information in areas very close to the chamber walls, in which the origin of pre-ignition is assumed.…”

Transient Performance of Gas-Engine-Based Power System on Ships: An Overview of Modeling, Optimization, and Applications

“…Jan et al [91] investigated the influence of total and local air-fuel ratios in the pre-chamber on the engine misfire boundary to address this issue when using high-inert-content flare gases as fuel. Other solutions for speeding up the burning rate and enhancing ignition behavior by pre-chamber jets also work for avoiding misfires [92].…”