Study on the ignitability of a high-pressure direct-injected methane jet using a diesel pilot, a glow-plug, and a pre-chamber

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 compression ratio, high combustion pressures, lean operation, quantity regulation, among others. However, in contrast to diesel direct 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 three ignition strategies for direct injected high-pressure gas jets have been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. The first type of ignition system is a pilot injection with a liquid fuel, the second is a glow-plug located near the main gas jet, and the third system is a pre-chamber with a nozzle hole aimed at the main gas jet. Results show that all three strategies are feasible options under the studied conditions. Ignition by a pilot fuel injection is a safe and reliable way to ignite the main fuel. The glow-plug is less reliable and leads to high cycle-to-cycle variation. The best option in the present study is the pre-chamber, it is very reliable, delivers the highest peak cylinder pressure and exhibits the lowest cyclic variability. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

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

“…The work presented by Vera-Tudela et al 2 showed the feasibility of using a pre-chamber system to ignite a high-pressure methane jet. It remains to be seen if the superior performance of the pre-chamber setup as shown in those experiments can be replicated in real engines where only one or two of the main gas jets can be ignited with a single pre-chamber.…”

“…As in the preceding study, 2 the experiments were performed in the Flex-OeCoS optical engine test facility. 35 This test facility allows for a wide range of operation conditions, such as compression and combustion pressures up to 140 and 240 bar, respectively, working at end-of-compression temperatures between 700 K and 1000 K, tunable flow/turbulence by varying the motor speed between 300 and 1800 rpm, adjustable air charge composition and high variability pneumatic-driven valve trains.…”

“…[32][33][34] A recent own study has shown the feasibility of using a pre-chamber to ignite a high-pressure gas jet and how this strategy compares to more traditional alternatives such as pilot injection and glow plug. 2 As result, the pre-chamber approach seems to be the best option, as it proved to be a reliable ignition method that delivered the highest peak cylinder pressure and exhibited the lowest cyclic variability. Thus, this paper is a continuation focusing on this novel method to ignite a high pressure directly injected gas jet to gain deeper insight of the involved processes.…”

“…Although rising climate awareness and even more stringent emission regulations lead to a rising share of electric vehicles, the internal combustion engine will continue to play an important role particularly in the cargo transport area in the foreseeable future. 1,2 By switching to low-carbon fuels like natural gas, CO 2 emissions are much reduced, corresponding exhaust gas aftertreatment systems are much less costly as well or can be omitted completely in gas-only engines. Moreover, natural gas contains methane from 60% to 90% which can be blended by any amount with renewable methane.…”

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

“…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.…”