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Effects of Variations in Market Gasoline Properties on HCCI Load Limits

BP-Yi Xu
Ford Powertrain Research and Advanced Engineering-Thomas Kenney
Published 2007-07-23 by SAE International in United States
The impact of market-fuel variations on the HCCI operating range was measured in a 2.3L four-cylinder engine, modified for single-cylinder operation. HCCI combustion was achieved through the use of residual trapping. Variable cam phasing was used to maximize the load range at each speed. Test fuels were blended to cover the range of variation in select commercial fuel properties. Within experimental measurement error, there was no change in the low-load limit among the test fuels. At the high-load limit, some small fuel effects on the operating range were observed; however, the observed trends were not consistent across all the speeds studied.
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On HCCI Engine Knock

Jialin Yang
Ford Research and Advanced Engineering-Thomas Kenney
Published 2007-07-23 by SAE International in United States
Knock in a HCCI engine was examined by comparing subjective evaluation, recorded sound radiation from the engine, and cylinder pressure. Because HCCI combustion involved simultaneous heat release in a spatially large region, substantial oscillations were often found in the pressure signal. The time development of the audible signal within a knock cycle was different from that of the pressure trace. Thus the audible signal was not the attenuated transmission of the cylinder pressure oscillation but the sound radiation from the engine structure vibration excited by the initial few cycles of pressure oscillation. A practical knock limited maximum load point for the specific 2.3 L I4 engine under test (and arguably for engines of similar size and geometry) was defined at when the maximum rate of cycle-averaged pressure rise reached 5 MPa/ms.
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Effect of Air Temperature and Humidity on Gasoline HCCI Operating in the Negative-Valve-Overlap Mode

Jialin Yang
Ford Research and Advanced Engineering-Thomas Kenney
Published 2007-04-16 by SAE International in United States
The impact of intake air temperature and humidity on gasoline HCCI engine operation was assessed. The 2.3 L I4 production engine modified for single cylinder operation was controlled by using variable cam phasing on both the intake and exhaust valve in the negative-valve-overlap mode. Exhaust cam phasing was mainly used to control load, and intake cam phasing was mainly used to control combustion phasing. At stoichiometric condition, higher intake air temperature advanced combustion phasing and promoted knock, resulting in a 19% reduction of the Net Indicated Mean Effective Pressure (NIMEP) at the high load limit at 1500 rpm when intake temperature was changed from −10 to 100° C. Higher ambient humidity delayed combustion phasing. For stoichiometric operation, this delay allowed a small extension (a few tenths of a bar in NIMEP) in the high load limit when the moisture concentration was changed from 3 to 30 g/m3 (corresponding to 10-100% relative humidity at 28° C). The low load limit was not sensitive to the ambient temperature and humidity because of the high level of residual…
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Robustness and Performance Near the Boundary of HCCI Operating Regime of a Single-Cylinder OKP Engine

Ford Motor Co.-Jialin Yang, Thomas Kenney
Published 2006-04-03 by SAE International in United States
A single-cylinder OKP (optimized kinetic process) engine, which uses homogeneous-charge compression-ignition (HCCI) technology, was tested, following a previous study, to evaluate the combustion system robustness and to improve the engine performance near the boundaries of the HCCI operating regime at light loads, high loads and high speed.To evaluate the robustness of HCCI combustion control, gasoline fuels with different RON were used, and the engine was tested at different coolant temperatures. It was demonstrated that the proposed HCCI control approaches could control the OKP engine system to operate robustly using different fuels and at different coolant temperatures.The effects of fuel injection timing and residual gas fraction on HCCI combustion and emissions, especially CO emissions and combustion efficiency, were tested at light loads; and the mechanisms were analyzed. At high loads, the effects of intake pressure and residual gas fraction on the combustion rate, knocking tendency, NOx emissions and the sensitivity of HCCI combustion timing control were investigated. The HCCI combustion-timing-control sensitivity at different engine speeds was also evaluated. Knowledge from this study may help in improving…
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Some Concepts of DISI Engine for High Fuel Efficiency and Low Emissions

Ford Motor Co.-Jialin Yang, Thomas Kenney
Published 2002-10-21 by SAE International in United States
Stratified-charge DISI engines have been launched in the market by Mitsubishi, Toyota, and Nissan. This paper discusses the current production stratified-charge DISI systems and some alternative systems, including the system using air-forced fuel injection and a proposed system that uses a swirl flow in the piston bowl with a special shape to separate the fuel-rich mixture layer from the wall surface. New DISI concepts are proposed to overcome some drawbacks of current bowl-in-piston type stratified-charge DISI systems. Charge stratification can be realized by using a soft spray with proper spray penetration, droplet size, and cone angle, as shown by CFD simulation results. The drawbacks of fuel wall wetting, soot limited load with charge stratification, large surface to volume ratio, etc., of the bowl-in-piston type system can be minimized. Bench tests with a conventional DI swirl-type injector showed that a liquid spray impinging on a semispherical target could produce a suitable soft spray fuel cloud. Finally, an engine combining homogeneous-charge DISI and variable valve timing may achieve the same fuel efficiency level as an emission constrained…
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Development of a Gasoline Engine System Using HCCI Technology - The Concept and the Test Results

Ford Motor Co.-Jialin Yang, Todd Culp, Thomas Kenney
Published 2002-10-21 by SAE International in United States
Homogeneous-charge compression-ignition (HCCI) technology has high potential to significantly reduce fuel consumption and NOx emissions over PFI engines. Control of the HCCI combustion process over the full range of conventional PFI operating conditions, however, has been a challenge. This study describes an HCCI-SI dual-mode engine system proposal based on new approaches to optimize the engine performance. A 0.658L single-cylinder engine was built and tested using these concepts. The engine was operated in HCCI mode from idle to 5.5 bar NMEP and up to 4750 rpm. NSFC in HCCI mode was about 175 g/kWh over most of the operating range except at very low load or near the high load boundary. At a part load of 1500 rpm and an equivalent BMEP of 2.62 bar, net indicated fuel efficiency was 50% higher than PFI engines and 30% higher than a prototype SC-DISI engine. Net specific NOx emissions were lower than 0.1 g/kWh below 4 bar NMEP, approximately two orders of magnitude lower than those from both SC-DISI and PFI engines. Boosting the intake pressure at loads…
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