This paper reviews progress on turbulent jet ignition systems for otherwise standard spark ignition engines, with focus on small pre-chamber systems (<3% of clearance volume) with auxiliary prechamber fueling. The review covers a range of systems including early designs such as those by Gussak and Oppenheim and more recent designs proposed by GM, FEV, Bosch and MAHLE Powertrain. A major advantage of jet ignition systems is that they enable very fast burn rates due to the ignition system producing multiple, distributed ignition sites, which consume the main charge rapidly and with minimal combustion variability. The locally distributed ignition sites allow for increased levels of dilution (lean burn/EGR) when compared to conventional spark ignition combustion. Dilution levels are comparable to those reported in recent homogeneous charge compression ignition (HCCI) systems. In addition, jet ignition systems have the potential for combustion phasing control and hence speed/load range benefits when compared to HCCI, without the need for SI-HCCI combustion mode switching. The faster burn rates also allow for a base compression ratio increase (1-2 points) when compared to spark ignition and when combined with diluted mixture combustion, provide increased engine efficiency.

A Review of Pre-Chamber Initiated Jet Ignition Combustion Systems

To ensure that private cars can continue to be used in the future, they must become significantly more efficient and at the same time emit considerably less pollutants. In addition to pure electric...

Analysis of experimental results with an active pre-chamber ultra-lean burn SI engine:

The research on two-stroke engines has been focused lately on the development of direct injection systems for reducing the emissions of hydrocarbons by minimizing the fuel short-circuiting. Low temperature combustion (LTC) may be the next step to further improve emissions and fuel consumption; however, LTC requires unconventional ignition systems. Jet ignition, i.e., the use of prechambers to accelerate the combustion process, turned out to be an effective way to perform LTC. The present work aims at proving the feasibility of adopting passive prechambers in a high-pressure, direct injection, two-stroke engine through non-reactive computational fluid dynamics analyses. The goal of the analysis is the evaluation of the prechamber performance in terms of both scavenging efficiency of burnt gases and fuel/air mixture formation inside the prechamber volume itself, in order to guarantee the mixture ignitability. Two prechamber geometries, featuring different aspect ratios and orifice numbers, were investigated. The analyses were replicated for two different locations of the injection and for three operating conditions of the engine in terms of revolution speed and load. Upon examination of the results, the effectiveness of both prechambers was found to be strongly dependent on the injection setup.

CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine

The aim of this project is to explore and understand the combustion phenomenon in engines operating on gaseous fuels, and develop technologies as an alternative to the present diesel engine technologies for heavy duty applications; which are facing severe challenges like stringent emissions norms, high technology costs and unsustainable fuel supply. The studies presented in this thesis focus on the application of pre-chamber ignition system in heavy duty natural gas engines, as a means to improve fuel efficiency and reduce NOx emissions. Initial experiments using pre-chamber spark plugs without auxiliary fueling showed improvements in combustion stability, but with only a marginal extension in the dilution limit with excess air and EGR; and hence no significant fuel efficiency improvements. Following these observations, a literature survey was conducted and it was soon realized that additional fueling to the pre-chamber will help scavenge the pre-chamber at the beginning of every cycle and also lead to the formation of an easily combustible mixture inside the pre-chamber, even while the main chamber is extremely fuel-lean. Further experiments conducted on a single cylinder engine with a custom made pre-chamber assembly with auxiliary fueling showed considerable extension of the dilution limit of main chamber combustion, from an excess air ratio of about 1.7 (with an un-fueled pre-chamber) to over 2.6. The maximum indicated efficiency observed at an operating load of 10 bar IMEPg was over 47% with engine-out NOx emission levels below the 'EURO 6' limits (for heavy duty natural gas engines). Following these finding, experiments to study the effect of pre-chamber volume and nozzle diameter on resulting main chamber ignition were conducted, where the pre-chamber volume fraction of 2.4% and the nozzle diameter ratio in the range of 0.025-0.035 (1/cm) were found to be optimum. CFD simulations were then conducted to understand the fluid dynamic aspects of interactions between the pre-chamber jets and the main chamber charge, which revealed the importance of jet momentum and jets-wall interaction on main chamber ignition. Further experiments on a large bore marine engine to understand scaling requirements for pre-chamber design showed that the optimal pre-chamber volume (and with it the nozzle diameter) scales with the displacement volume of the engine. Gross indicated efficiency of 50% was also recorded. (Less)

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Improving the Efficiency of Gas Engines using Pre-chamber Ignition

Chowdhury, M Arshad Zahangir. M.S.M.E., Purdue University, August 2018. Traversing Hot Jet Ignition Delay of Hydrocarbon Blends in a Constant Volume Combustor. Major Professor: M. Razi Nalim. A chemically reactive turbulent traversing hot-jet issued from a pre-chamber to a relatively long combustion chamber is experimentally investigated. The long combustion chamber represents a single channel of a wave rotor constant-volume combustor. The issued jet ignites the fuel-air mixture in the combustion chamber. Fuel-air mixtures are prepared with different hydrocarbon fuels of different reactivity, namely, methane, propane, methane-hydrogen blend, methane-propane blend and methaneargon blend. The jet acts as a rapid, distributed and moving source of ignition, traversing across one end of the long combustion chamber entrance, induces complex flow structures such as a train of counter rotating vortices that enhance turbulent mixing. In general, a stationary hot-jet ignition process lack these structures due to absence of the traversing motion. The ignition delay of the fuels and fuel blends are measured in order to obtain insights about constant-volume pressure-gain combustion process initiated by a moving source of ignition and also to glean useful data about design and operation of a wave rotor combustor. Reactive hot-jets are useful to ignite fuel-air mixtures in internal combustion engines and novel wave rotor combustors. A reactive hot-jet or puff of gas issued from a suitably designed pre-chamber can act as rapid, distributed and less polluting ignition source in internal combustion engines. Each cylinder of the engine is provided with its own pre-chamber. A wave rotor combustor has an array of circumferentially arranged channels on a rotating drum. Each channel acts as a constant-volume combustor and produces high pressure combustion products. Implementation of hot-jet igniter in a wave rotor combustor offers utilization of available high temperature and

T. Ken Garrett

Papers

Porsche stratified charge engine