Kelvin Xie

Speciation Analysis of Light Hydrocarbons and Hydrogen Production During Diesel Low Temperature Combustion

The simultaneous reduction in engine-out NOx and soot emissions with diesel low temperature combustion (LTC) is generally accompanied by high levels of hydrocarbon (THC) and carbon monoxide (CO) emissions in the exhaust. To achieve clean diesel combustion in terms of low regulated emissions (NOx, soot, THC, and CO), the exhaust combustibles must be dealt with the exhaust aftertreatment (typically a diesel oxidation catalyst). In this work, engine tests were performed to realize LTC on a single-cylinder common-rail diesel engine up to 12 bar IMEP. A single-shot fuel injection strategy was employed to push the diesel cycles into LTC with exhaust gas recirculation (EGR). The combustibles in the exhaust were generally found to increase with the LTC load and were observed to be a function of the overall equivalence ratio. A Fourier transform infrared (FTIR) spectroscopy analysis of light hydrocarbon emissions found methane to constitute a significant component of the hydrocarbon emissions under the tested LTC conditions. The relative fraction of individual species in the hydrocarbons also changed, indicating a richer combustion zone and a reduction in engine-out THC reactivity. The hydrogen production was found to correlate consistently with the CO emissions, largely independent of the boost pressure or engine load under the tested LTC conditions. This research intends to identify the major constituents of the THC emissions and highlight the possible impact on exhaust aftertreatment.© 2011 ASME

An Analysis of the Production of Hydrogen and Hydrocarbon Species by Diesel Post Injection Combustion

The effects of post injection on the combustion efficiency, exhaust emissions, and in-cylinder hydrogen generation were experimentally investigated in a modern heavy duty diesel engine. As the post injection was moved away from top dead center (TDC), the test results generally showed increasing carbon monoxide (CO) and total hydrocarbons (THC), fairly constant nitrogen oxide (NOx) emissions while the smoke emissions were more sensitive to the post injection timing. Hydrogen production was observed to be higher at later post injection timings. In a majority of instances, hydrogen production and carbon monoxide formation were very well correlated. Additional tests explored the effects of the overall air-to-fuel ratio on the in-cylinder hydrogen production and the experimental results indicated that a lower air-to-fuel ratio seemed to promote the in-cylinder generation of hydrogen. However, the increased hydrogen production was offset by less efficient power production from the post injection combustion. A Fourier transform infrared (FTIR) spectroscopy analysis of hydrocarbon emissions was carried out in an attempt to determine the effects of diesel post injection timing on individual light hydrocarbon species.Copyright

Characterization of N-Butanol High Pressure Injection From Modern Common Rail Injection System

Increasing attention has being paid to alternative fuels that have the potential to reduce overall greenhouse gas emissions and fossil fuel dependence. The alcohol fuel n-butanol, as one of the advanced biofuels, can be potentially utilized as a partial or complete substitute for the diesel fuel in diesel engines. Experimental results from literature, as well as from the authors’ previous research, have shown promising trend of low soot and nitrogen oxides emissions from the combustion with n-butanol high pressure direct injection. However, due to the significant fuel property differences between n-butanol and diesel, the fuel delivery mechanism and combustion control algorithm need to be optimized for n-butanol use. A better understanding of the high pressure n-butanol injection characteristics, such as the injector opening/closing delays and spray droplet sizes, can provide the guidance for the control optimization and insights to the empirical observations of engine combustion and emissions. Meanwhile, the experimental data could be used for the model development of the n-butanol high pressure fuel injection events.In this work, injection rate measurement, high-speed video direct imaging, and phase Doppler anemometry (PDA) analysis of neat n-butanol and diesel fuel have been conducted with a light-duty high pressure common-rail fuel injection system. The injection rate measurement was performed with an offline injection rate analyzer at 20 bar backpressure to obtain the key parameters of the injector opening/closing delays, and the instantaneous pressure rise. The spray direct imaging was carried out in a pressurized chamber, and the PDA measurement was conducted on a test bench at ambient temperature and pressure. The injector dynamics and spray behavior with respect to the different fuels, variation of injection pressures, and variation of injection durations are discussed.Copyright

A Study of Combustion Inefficiency in Diesel LTC and Gasoline-Diesel RCCI via Detailed Emission Measurement

Reduction of engine-out NOx emissions to ultra-low levels is facilitated by enabling low temperature combustion (LTC) strategies. However, there is a significant energy penalty in terms of combustion efficiency as evidenced by the accompanying high levels of hydrocarbon (HC), carbon monoxide (CO), and hydrogen emissions. In this work, the net fuel energy lost as a result of incomplete combustion in two different LTC regimes is studied. The first LTC strategy, partially premixed compression ignition (PPCI), is investigated using a single, high pressure, in-cylinder injection of diesel fuel along with the application of exhaust gas recirculation (EGR). The second strategy includes dual-fuel application – reactivity controlled compression ignition (RCCI) of port injected gasoline and direct injected diesel. Moderate to high levels of EGR are necessary during engine operation in either of the two LTC pathways. A detailed analysis of the incomplete combustion products was conducted while the engine was operated in the aforementioned LTC modes. Speciation analysis of hydrocarbons was performed by sampling the exhaust gas in an FTIR. The total HC and the CO emissions were simultaneously measured using an FID and an NDIR, respectively. The production of hydrogen during the combustion process was also evaluated using a mass spectrometer. Engine tests were conducted at a baseline load level of 10 bar IMEP in the PPCI and RCCI modes. Load extension tests, up to 17 bar IMEP, were then conducted in the RCCI mode by increasing the gasoline-to-diesel fuel ratio. Test results indicated that CO, H2, and light HC made up for most of the combustion in-efficiency in the PPCI mode while heavier HC and aromatics were significantly higher in the RCCI mode.Copyright

Multi-Coil High Frequency Spark Ignition to Extend Diluted Combustion Limits

A reliable ignition process is desirable for the ignition of a lean and/or EGR diluted cylinder charge commonly adopted to achieve clean and efficient engine combustion. In this work, ignition of a diluted propane-air mixture is investigated using a high energy spark ignition system. Efforts are dedicated towards development of a novel ignition system that improves the ignition quality whilst keeping within the bounds of current spark ignition hardware to facilitate potential application in future clean combustion engines. A multi-coil ignition system was developed to adjust the spark energy and the discharge pattern. With enhanced primary voltage up to 120 V, a multi-spark strategy with frequency up to 20 kHz can be implemented. The combustion visualization results show that the application of both multi-coil and multi-spark strategy can promote the flame propagation. The high frequency multi-spark strategy shows better ignition quality compared to a single-spark strategy. With discharge energy enhancement by coupling more coils, the ignition success rate is increased under diluted mixture conditions. The diluted combustion limits are therefore extended with the help of these spark strategies.

A Preliminary Study of the Spark Characteristics for Unconventional Cylinder Charge With Strong Air Movement

Detailed fundamental understanding of spark discharge under strong air movement condition is crucial to optimize the ignition systems for stratified charge engines. In this paper, extensive bench tests of spark discharge under strong air movement condition are conducted by means of both optical and electrical diagnosis. Strong correlations between the physical structures of spark plasma channel and the gas velocity are found in this paper. The spark heat dissipation distance, the plasma stretched distance and the plasma area under various flow velocities are analyzed. The resistance between the electrode gaps is increased with the enhancement of flow velocity. As a result, the discharge voltage is enhanced, while the discharge duration is shortened. When the flow velocity is enhanced substantially, restrikes of spark discharge are observed. The increasing rate of the discharge voltage before the first restrike is found to be a 2-order polynomial relation to the gas velocity. With the enhancement of flow velocity, the delivered discharge energy increases linearly at the velocity below 25m/s, while it tends to be maintained at the higher flow velocities. Both the increase of the electrode gap size and the flow velocity shorten the spark discharge duration.Copyright

Light Hydrocarbon Emissions From Diesel Low Temperature Combustion

A modern common-rail diesel engine was used to investigate hydrocarbon emissions under low temperature diesel combustion conditions. In this work, various EGR ratios and fuel mixing strategies were applied under a series of fixed-load conditions to progressively lower the flame temperature, which is verified by progressively reduced NOx emission. During the tests, the concentrations of total hydrocarbons, representative light hydrocarbon species (methane, acetylene, and ethylene), and hydrogen gas were measured with a set of emission analyzers, FTIR, and H2 mass-spectrometer. The trend for light hydrocarbon emissions was identified to be a function of both load and EGR ratio. Hydrogen gas can be emitted in significant quantities with the application of very high EGR. Under ultra-low NOx production conditions for medium and high load conditions, the light hydrocarbon species can account for the majority of hydrocarbon emissions.© 2010 ASME