Influence of Early and Late Fuel Injection on Air Flow Structure and Kinetic Energy in an Optical SIDI Engine

The turbulent in-cylinder air flow and the unsteady high-pressure fuel injection lead to a highly transient air fuel mixing process in spark-ignition direct-injection (SIDI) engines, which is the leading cause for combustion cycle-to-cycle variation (CCV) and requires further investigation. In this study, crank-angle resolution particle image velocimetry (PIV) was employed to simultaneously measure the air flow and fuel spray structure at 1300 rpm in an optically accessible single-cylinder SIDI engine. The measurement was conducted at the center tumble plane of the four-valve pent-roof engine, bisecting the spark plug and fuel injector. 84 consecutive cycles were recorded for three engine conditions, i.e. (1) none-fueled motored condition, (2) homogeneous-charge mode with start of injection (SOI) during intake (50 crank-angle degree (CAD) after top dead center exhaust, aTDCexh), and (3) stratified-charge mode with SOI during mid compression (270 aTDCexh). The air flow structure (quantified by the objective metric – relevance index) and kinetic energy were examined to study the effect of the fuel spray on the air flow. The air flow was nearly identical for three conditions before the fuel injection. During fuel injection, the entrainment of air into the spray was observed near the spray but the flow structure further away from the spray was not significantly affected for both homogeneous and stratified charge modes. Right after the fuel was atomized, the spray increased the kinetic energy of air flow by 48±25% and 45±40% (average ± standard variation, with CCV included in standard deviation) for spray at intake and compression stroke, respectively. Spray changed the flow structure and kinetic energy immediately after injection for both conditions. The changes caused by injection during intake did not affect the flow and CCV at spark timing. For injection during mid compression, both the flow-structure and kinetic-energy CCV were apparently affected at spark timing.This work is supported by the Engine Systems Division of the General Motors – University of Michigan Automotive Collaborative Research Laboratory.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142812/1/2018-01-0205.pd

Characterization of the effect of intake air swirl motion on time-resolved in-cylinder flow field using quadruple proper orthogonal decomposition

The control of intake air swirl motion is often used in spark-ignition direct-injection (SIDI) engine to improve its in-cylinder fuel–air mixing process especially under engine idle and low load conditions. In this experimental investigation, a novel technique combining the time-resolved particle image velocimetry (PIV) with quadruple proper orthogonal decomposition (POD) is implemented to analyze the time-resolved in-cylinder velocity measurements in an optically-accessible SIDI engine. The intake air swirl motion is introduced into the engine cylinder by a control valve installed in one of two air intake ports. Experimental results show that a strong linear correlation exists between the intake flow swirl ratio and vorticity flow field in the cylinder. This correlation ensures high data reliability of swirl motion control and provides a novel basis to directly compare the flow field measurements under different swirl ratio conditions. The quadruple proper orthogonal decomposition analysis is then applied to the velocity flow fields to separate the highly dynamic in-cylinder flow characteristics into four distinct categories: (1) dominant flow structure; (2) coherent structure; (3) turbulent structure; and (4) noise structure. The results show that the dominant flow structure varies strongly with swirl ratio, and its kinetic energy is also directly related to the swirl ratio. The coherent structure captures the large scale flow characteristics, but its kinetic energy is much lower and exhibits larger cycle-to-cycle variations. The turbulent structure contains similar level of kinetic energy at different swirl ratios but without much cycle-to-cycle variation. Finally, the noise structure contains very low kinetic energy which only alters the dynamic nature of the flow field slightly. In summary, the effect of swirl ratio on in-cylinder flow field is mostly captured by the dominant flow structure and partially captured by the coherent flow structure. The turbulent flow structure can characterize the high-order flow variation. The noise structure can be neglected due to the low energy captured.This research is sponsored by General Motors Company (USA), and National Natural Science Foundation of China (NSFC), under grants No. 51176115/E060404. It was carried out at the National Engineering Laboratory for Automotive Electronic Control Technology of Shanghai Jiao Tong University. The technical support and discussions provided by Dr. Tang-wei Kuo, Dr. Xiaofeng Yang, and Dr. Cherian Idicheria of the Powertrain System Research Laboratory of General Motors Company are gratefully acknowledged.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142372/1/1-s2.0-S019689041501002X-main.pd

FUEL IMPINGEMENT ANALYSIS OF FLASH-BOILING SPRAY IN A SPARK-IGNITION DIRECT-INJECTION ENGINE

Fuel impingement has been recognized as one of the major causes for the soot formation in spark-ignition direct-injection (SIDI) engines. Previous study demonstrated that flash-boiling fuel spray provided desirable spray structure with shorter penetration, more homogeneous fuel distribution, smaller droplets and better evaporation. However, it is still unknown whether the flash-boiling spray is capable of reducing fuel impingement compared with the conventional non-flash-boiling spray. In this study, crank-angle resolved Mie-scattered spray images for multiple cycles are recorded to investigate the spray impingement phenomenon in an optical SIDI engine for both the non-flash-boiling spray and flash-boiling spray. An eight-hole direct-injection injector is utilized, and gasoline fuel is heated to achieve flash-boiling spray condition. Image processing algorithm is developed to reveal the fuel impingement in a quantitative manner. It is found that the flash-boiling spray is effective to reduce the overall fuel impingement. In addition, the cycle-to-cycle variation of fuel impingement is demonstrated for both the non-flash-boiling spray and flash-boiling spray.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140986/1/ChenH_ILASS-Asia2013.pdfDescription of ChenH_ILASS-Asia2013.pdf : Conference proceedin

Fast Bidirectional Motion Planning for Self-Driving General N-Trailers Vehicle Maneuvering in Narrow Space

Self-driving General N-trailers (GNT) vehicles are one of the future solutions to build intelligent factory due to its flexibility and large load. Maneuvering of GNT vehicle to its destination requires accurate and robust motion planning. But the narrow operating environment causes nonlinear nonconvex constraints which are challenging. Furthermore, the nonholonomic constraints in GNT kinematics elevate the complexity in state space. Therefore, motion planning of GNT vehicle maneuvering in narrow space within a reasonable time and high success rate is a critical problem. This paper proposes a fast bidirectional motion planning algorithm to generate trajectories for GNT vehicles to maneuver in a narrow space. A coarse-to-fine motion planning paradigm has been proposed to balance the robustness and time. In the coarse step, an initial guess is generated through a bidirectional-sampled closed-loop Rapidly-exploring Random Tree, and a spatial-temporal safety corridor has been constructed to convert nonlinear nonconvex constraints to linear convex constraints. In the fine step, an optimal control problem is defined accordingly and solved to obtain feasible trajectory. Four different scenarios have been conducted with forward and reverse GNT vehicle maneuvering in a narrow environment. The results show that the proposed method outperforms state-of-the-art sampling-based and optimization-based motion planning methods

Laser Irradiation Behavior of Carbon Fiber Epoxy Resin Composites with Laminar Structure

Laser attracts more attention and it could cause material failure by its high energy. Carbon fiber resin composites are widely used in aerospace vehicles experiencing dramatic damage to their surface if exposed to high-energy laser irradiation. The available studies on irradiation behavior are mainly focused on pulsed lasers and bulk composites, and investigations of thin laminar structures under continuous-wave laser irradiation have rarely been reported. In this study, the damage behavior of laminar carbon fiber epoxy resin composites (CFE composites) was studied. Using a threshold model of resin pyrolysis, CFE composite is observed to be damaged at 0.18 s when irradiated at 100 W/cm2, and if the laser power density is increased to 200 W/cm2 for 2 s, no resin remains on the fiber surface, which is now completely exposed. With an increase in power density and irradiation time, the ablation rate always shows an upward trend: the ablation region expands and the separation of layers in the interior appears, which can reach 0.01156 g/s when irradiated at 100 W/cm2 for 5 s. The damage mechanism of CFE composite was also revealed by the temperature evolution data, thermogravimetric analysis, and composition change

Laser Irradiation Behavior of Carbon Fiber Epoxy Resin Composites with Laminar Structure

Laser attracts more attention and it could cause material failure by its high energy. Carbon fiber resin composites are widely used in aerospace vehicles experiencing dramatic damage to their surface if exposed to high-energy laser irradiation. The available studies on irradiation behavior are mainly focused on pulsed lasers and bulk composites, and investigations of thin laminar structures under continuous-wave laser irradiation have rarely been reported. In this study, the damage behavior of laminar carbon fiber epoxy resin composites (CFE composites) was studied. Using a threshold model of resin pyrolysis, CFE composite is observed to be damaged at 0.18 s when irradiated at 100 W/cm2, and if the laser power density is increased to 200 W/cm2 for 2 s, no resin remains on the fiber surface, which is now completely exposed. With an increase in power density and irradiation time, the ablation rate always shows an upward trend: the ablation region expands and the separation of layers in the interior appears, which can reach 0.01156 g/s when irradiated at 100 W/cm2 for 5 s. The damage mechanism of CFE composite was also revealed by the temperature evolution data, thermogravimetric analysis, and composition change