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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 and emission characteristics of transient turbulent gaseous fuel jets in heated and compressed air was conducted in a shock tube facility. Experiments were performed at an initial pressure of 30 bar with initial oxidizer temperatures ranging from 1200 to 1400 K, injection pressures ranging from 60 to 150 bar, and injection durations ranging from 1.0 to 2.5 ms. Methane and 90.0% methane/10.0% ethane blend were used as fuel. Under the operating conditions studied, increasing temperature resulted in a significant decrease in autoignition delay time. Increasing the injection pressure decreased ignition delay as well. The downstream location of the ignition kernel relative to the jet penetration distance was found to be in the range, 0.4

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.

The use of exhaust gas recirculation (EGR) to control NOx emissions from direct-injection engines results in the reintroduction of exhaust particulate matter (PM) into the intake manifold. The influence of this recirculated PM on emissions from a pilot-ignited direct injection of natural gas engine was studied by installing a filter in the EGR system. Comparison tests at fixed engine conditions were conducted to identify differences between filtered and unfiltered EGR. No significant variations in gaseous or PM mass emissions were detected. This indicates that the recirculated PM is not contributing substantially to the increases in PM mass emissions commonly observed with EGR. Reductions in black carbon and ultra-fine particle exhaust concentrations in the exhaust were observed at the highest EGR fractions with the filter installed.

A diesel pilot-ignited, high-pressure direct-injection of natural gas heavy-duty single-cylinder engine was fuelled with both natural gas and blends of 10% and 23% by volume hydrogen in methane. A single operating condition (6 bar GIMEP, 0.5 ϕ, 800 RPM, 40%EGR) was selected, and the combustion phasing was varied from advanced (mid-point of combustion at top-dead-center) to late (mid-point of combustion at 15°ATDC). Replacing the natural gas with hydrogen/methane blend fuels was found to have a significant influence on engine emissions and on combustion stability. The use of 10%hydrogen was found to slightly reduce PM, CO, and tHC emissions, while improving combustion stability. 23%hydrogen was found to substantially reduce CO and tHC emissions, while slightly increasing NOx. The greatest reductions in CO and tHC, along with a significant reduction in PM, were observed at the latest combustion timings, where combustion stability was lowest.

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.

The use of pilot-ignited, direct-injected natural gas in a heavy-duty compression-ignition engine has been shown to reduce emissions while maintaining performance and efficiency. Adding recirculated exhaust gas (EGR) has been shown to further reduce emissions of nitric oxides (NOx), albeit at the cost of increased hydrocarbons (tHC), carbon monoxide (CO), and particulate matter (PM) emissions at high EGR fractions. Previous tests have suggested that reducing the delay between the diesel and natural gas injections, increasing the injection pressure, or adjusting the combustion timing have individually achieved substantial emissions benefits. To investigate the effectiveness of combining these techniques, and of using them over a wide range of operating conditions, a series of tests were carried out. The first set of tests investigated the interactions between these effects and the EGR fraction.

Determining what exhaust gas recirculation (EGR) control parameters have the largest impact on engine performance and emissions is of critical importance when developing an EGR-equipped engine. These tests studied the effects of varying the net charge mass, the fresh air charge mass, the indicated power, and the oxygen equivalence ratio at various EGR fractions. The research was carried out on a direct-injection, natural gas fuelled, pilot-ignited four-stroke heavy-duty engine using Westport Innovations Inc.'s pilot-ignited, direct injection of natural gas technology. The testing was carried out using a prototype injector and the standard diesel-fuelled engine's combustion chamber. The results indicate that fuel efficiency, as well as emissions of Nitrogen Oxides (NOx) and Carbon Monoxide (CO) depend primarily on the EGR level, and not on the values of the EGR control parameters.

Pilot-ignited direct injection of natural gas fuelling of a heavy-duty compression ignition engine while using recirculated exhaust gas (EGR) has been shown to significantly reduce NOx emissions. To further investigate emissions reductions, the combustion timing, injection pressure, and relative delay between the pilot and main fuel injections were varied over a range of EGR fractions while engine speed, net charge mass, and oxygen equivalence ratio were held constant. PM emissions were reduced by higher injection pressures without significantly affecting NOx at all EGR conditions. By delaying the combustion, NOx was reduced at the expense of increased PM for a given EGR fraction. By reducing the delay between the pilot and main fuel injections at high EGR, PM emissions were substantially reduced at the expense of increased total hydrocarbon (tHC) emissions. In this research, no attempt was made to optimize the injector or combustion chamber for natural gas fuelling with EGR.