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Measurements of ignition characteristics and emissions were made in a shock tube facility operating at engine-relevant conditions. Methane and methane/ethane fuels were injected down the centerline of the shock tube using an electronically controlled prototype gaseous fuel injector developed by Westport Innovations. Air was preheated and compressed using a reflected shock technique that produced run times of 4-5 ms. Particulate matter (PM) emissions were found to be highly intermittent. In only 6 out of 97 experiments was PM detected above background levels. In all of these 6 sooting experiments ignition kernels were located relatively close to the injector tip and ignition occurred prior to the end of fuel injection. Using the large orifice injector tip with pure methane fuel, PM was detected in 4 out of 28 experiments; using the small orifice with pure methane fuel, no PM was detected in any of 50 experiments.

Conditional source-term estimation (CSE) is a novel chemical closure method for the simulation of turbulent combustion. It is less restrictive than flamelet-based models since no assumption is made regarding the combustion regime of the flame; moreover, it is computationally cheaper than conventional conditional moment closure (CMC) models. To date, CSE has only been applied for simulating canonical laboratory flames such as steady Bunsen burner flames. Industry-relevant problems pose the challenge of accurately modelling a transient ignition process in addition to involving complex domaingeometries. In this work, CSE is used to model combustion in a homogeneous-charge natural gas fuelled SI engine. The single cylinder Ricardo Hydra research engine studied here has a relatively simple chamber geometry which is represented by an axisymmetric mesh; moving-mesh simulations are conducted using the open-source computational fluid dynamics software, OpenFOAM.

An experimental investigation of the autoignition of transient gaseous fuel jets in heated and compressed air is conducted in a shock tube facility. Experiments are performed at an initial pressure of 30 bar with initial oxidizer temperatures ranging from 1150 K to 1400 K, injection pressures ranging from 60 bar to 150 bar, and with injector tip orifice diameters of 0.275 mm and 1.1 mm. Under the operating conditions studied, increasing temperature results in a significant decrease in autoignition delay time, td. The smaller orifice results in an increase in ignition delay time and variability, as compared with the larger orifice. For initial temperatures below about 1250K, ignition is rarely achieved with the smaller orifice, whereas ignition is always achieved with the larger orifice down to 1150 K. Under the conditions studied, increasing the injection pressure decreases ignition delay, a result dynamically consistent with larger orifice size decreasing ignition delay time.