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Now showing items 1 - 16 of 150

  • Back pressure effect on three-way catalyst light-off

    Baron, Jan H.   Cheng, Wai K.  

    The effect of back pressure on the light-off of a modern spark ignition engine three-way catalyst has been assessed by measuring the hydrocarbon conversion efficiency in a hot flow bench and in the cold-idle period in an engine. In the flow bench experiment, a small amount of propane/air mixture is used as a surrogate for the hydrocarbon mixture. The conversion efficiency is found to be only a function of temperature. The efficiency is independent of pressure, space velocity, and the equivalence ratio of the hydrocarbon mixture for lambda >=3D 1. In the engine test, while the engine-out exhaust gas temperature is higher at a higher back pressure, there is little difference between the gas temperatures at the catalyst entrance for different back pressures at retarded spark timing. This observation is attributed to the larger amount of exhaust hydrocarbon conversion oxidation between the engine exit and the catalyst entrance with the lower back pressure. The heat release from this oxidation compensates for the lower engine-out exhaust temperature at the lower back pressure. The catalyst temperature increases modestly and light-off time shortens correspondingly at the higher back pressure. This observation is attributed solely to the increase in mass flow rate (and thus exhaust sensible enthalpy flow rate) of the engine needed to overcome the additional pumping loss due to the throttling of the exhaust. These results have been confirmed with a simple one-dimensional catalyst model.
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  • Fuel carbon pathway in the first cranking cycle of a gasoline direct injection engine

    Rodriguez, J. Felipe   Cheng, Wai K.  

    The fuel carbon pathway for the cold-start first cranking cycle in a gasoline direct injection engine is characterized quantitatively. The engine is fired for a single cycle in one cylinder at a specified cranking speed and at a coolant temperature of 20 degrees C. The fuel carbon is accounted for from measurements of the exhaust carbon (CO2, CO, and hydrocarbon). The remaining carbon is assumed to go into the oil and crankcase. The parameters studied are the amount of injected fuel, the injection timing, the intake pressure, the injection pressure, and the cranking speed. Substantial fuel enrichment is needed to produce stable combustion in the first cycle, with significant residual fuel that goes into preparing the mixture of the second cycle and into the oil and crankcase. The first cycle hydrocarbon emissions as a fraction of the fuel are not sensitive to the fuel enrichment, the manifold absolute pressure, and the injection pressure.
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  • The engine reformer:Syngas production in an engine for compact gas-to-liquids synthesis

    Lim, Emmanuel G.   Dames, Enoch E.   Cedrone, Kevin D.   Acocella, Angela J.   Needham, Thomas R.   Arce, Andrea   Cohn, Daniel R.   Bromberg, Leslie   Cheng, Wai K.   Green, William H.  

    Methane (CH4) reforming was carried out in an internal combustion engine (an engine reformer). We successfully produced syngas from the partial oxidation of natural gas in the cylinder of a diesel engine that was reconfigured to perform spark ignition. Performing the reaction in an engine cylinder allows some of the exothermicity to be captured as useful work. Intake conditions of 110kPa and up to 480 degrees C allowed low cycle-to-cycle variability (COVnimep <20%) at methane-air equivalence ratios (phi(M)) of 2.0, producing syngas with an H-2-to-CO ratio of 1.4. Spark ignition timing was varied between 45-30 degrees before top-dead-center (BTDC) piston position, showing significant improvement with delayed timing. Hydrogen (H-2) and ethane (C2H6) were added to simulate recycle from a downstream synthesis reactor and realistic natural gas compositions, respectively. Adding these gases yielded a stable combustion up to hydrocarbon-air equivalence ratios (phi(HC)) of 2.8 with COVnimep<5%. Ethane concentrations (with respect to methane) of up to 0.2L/L (20vol%) (with and without H-2) produced robust and stable combustions, demonstrating that the engine can be operated across a range of natural gas compositions. Engine exhaust soot concentrations demonstrated elevated values at phi(HC)>2.4, but <1mg/L below these equivalence ratios. These results demonstrate that the engine reformer could be a key component of a compact gas-to-liquids synthesis plant by highlighting the operating conditions under which high gas conversion, high H(2-)to-CO ratios close to 2.0, and low soot production are possible.
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  • Potential of Negative Valve Overlap for Part-Load Efficiency Improvement in Gasoline Engines

    Rodriguez, J. Felipe   Cheng, Wai K.  

    This article reports on the potential of negative valve overlap (NVO) for improving the net indicated thermal efficiency (eta( NIMEP)) of gasoline engines during part load. Three fixed fuel flow rates, resulting in indicated mean effective pressures of up to 6 bar, were investigated. At low load, NVO significantly reduces the pumping loses during the gas exchange loop, achieving up to 7% improvement in indicated efficiency compared to the baseline. Similar efficiency improvements are achieved by positive valve overlap (PVO), with the disadvantage of worse combustion stability from a higher residual gas fraction (x(r)). As the load increases, achieving the wide-open throttle limit, the benefits of NVO for reducing the pumping losses diminish, while the blowdown losses from early exhaust valve opening (EVO) increase. However, a symmetric NVO strategy combined with a shorter exhaust duration has a higher potential for reduction in part-load fuel consumption, as the EVO timing can be optimized to minimize the blowdown losses.
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  • The fast-response flame ionization detector

    Cheng, Wai K.   Summers, Tim   Collings, Nick  

    The fast-response flame ionization detector has become a widely used instrument for time-resolved hydrocarbon measurements in internal combustion engines. The characteristics of and working experience with the instrument are reviewed. In particular, the sampling system and its performance for isolating the pressure pulsation in in-cylinder and in engine exhaust measurements are described. Results from different applications are given to illustrate the utilities of the instrument.
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  • A study of soot formation in a rapid compression machine at conditions representative of cold-fast-idle in spark ignition engines

    Ketterer, Justin E.   Cheng, Wai K.  

    The soot yield, defined as the ratio of the soot mass to the carbon mass in the fuel, for the homogeneous combustion of a rich fuel-air mixture has been measured in a rapid compression machine using the laser light extinction method. The temperature and pressure conditions are representative of those in spark-ignition direct-injection engines at cold-fast-idle. The fuels used are a certification gasoline (with 28% aromatic content) and a blend of the gasoline with toluene (the blend had 40% aromatic content by volume) so that the sensitivity of soot formation to the fuel aromatic content could be assessed. Beyond a threshold fuel equivalence ratio (phi) value, the soot yield increases exponentially with phi. The soot yield of the gasoline-toluene blend is four to six times higher than that of the gasoline. The soot yield decreases exponentially with temperature, by a factor of 0.58 for every 10 K increase in temperature. In the 657-695 K temperature range, the threshold phi value increases linearly from approximately 2.4 to 2.7, at a rate of 0.1 point per 10 K rise in temperature. This temperature dependence is insensitive to the charge density.
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  • Global Production and Trade in East Asiaby L. K. Cheng; H. Kierzkowski

    Review by: Rama V. Ramachandran  

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  • Global Production and Trade in East Asiaby L. K. Cheng; H. Kierzkowski

    Review by: Rama V. Ramachandran  

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  • Reply to H-M Cheng and K Sundram

    Katan, Martijn B; Zock, Peter L; van de Bovenkamp, Peter; Hectors, Magda  

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  • Singapore Women: Three Decades of Change.by Aline K. Wong; Leong Wai Kum

    Review by: Jason Tan  

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  • UNDERSTANDING CHENG PROPOSAL, A RESPONSE TO IP,PO,K. + CHINESE SCIENCE

    SELLMAN, J   FLEMING, J  

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  • Pao-Lu Hsu: Collected Papersby K. L. Chung; C.-S. Cheng; T.-P. Chiang

    Review by: M. S. Bartlett  

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  • Pao-Lu Hsu: Collected Papersby K. L. Chung; C.-S. Cheng; T.-P. Chiang

    Review by: M. S. Bartlett  

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  • Three new taxane diterpenoids from the seeds of Taxus yunnanensis Cheng et L. K. Fu and T. cuspidata Sieb et Zucc

    Qing-wen Shi   Takayuki Oritani   Takeyoshi Sugiyama   Tohru Horiguchi   Ryo Murakami   Ding Zhao   Takashi Oritani  

    Chemical examination of the seeds of the Chinese yew, Taxus yunnanensis Cheng et L. K. Fu and Japanese yew, T. cuspidata Sieb et Zucc resulted in the isolation of three new and rare rearranged abeotaxane type of diterpenoids in addition to several known compounds. The structures of the new taxoids have been established as 9alpha, 13alpha-diacetoxy-11(15fwdarw1)abeotaxa-4(20), 11-diene-5alpha, 10beta, 15-triol (1), 9alpha, 13alpha-diacetoxy-10beta-benzoyloxy-5alpha-(3'-dimethylamino-3'-phenyl)- propionyloxy-11(15fwdarw1)abeotaxa-4(20), 11-diene-15-ol (2), and 2alpha,7beta,13alpha-triacetoxy-10beta-hydroxy-5alpha-(3'-dimethylamino- 3'-phenyl)-propionyloxy-2(3fwdarw20)-abeo-taxa-9-one (3) by a study of their spectral data.
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  • Three new taxane diterpenoids from the seeds of Taxus yunnanensis Cheng et L. K. Fu and T. cuspidata Sieb et Zucc

    Shi, Qing-wen   Oritani, Takayuki   Sugiyama, Takeyoshi   Horiguchi, Tohru   Murakami, Ryo   Zhao, Ding   et. al.  

    Chemical examination of the seeds of the Chinese yew, Taxus yunnanensis Cheng et L. K. Fu and Japanese yew, T. cuspidata Sieb et Zucc resulted in the isolation of three new and rare rearranged abeotaxane type of diterpenoids in addition to several known compounds. The structures of the new taxoids have been established as 9α, 13α-diacetoxy-10β-benzoyloxy-5α-(3′-dimethylamino-3′-phenyl)-propionyloxy-11(15→1)abeotaxa-4(20), 11-diene-15-ol (2), and 2α, 7β, 13α-triacetoxy-10β-hydroxy-5α-(3′-dimethylamino-3′-phenyl)-propionyloxy-2(3→20)-abeo-taxa-9-one (3) by a study of their spectral data.
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  • Brief Notes on K. G. Tregonning's "Tan Cheng Lock: A Malayan Nationalist"

    Agnes Tan  

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