End Of Intake Stroke Research Articles

Low-speed performance compensation of a turbocharged natural gas engine by intake strategy optimization

Power output at the low engine speed is limited for natural gas engines, even though the turbocharging technology is used. In this paper, the intake system of a turbocharged spark-ignition natural gas engine with 4 valves (2 intake valves and 2 exhaust valves) was optimized by considering the intake strategy effects on the engine torque output and fuel economy improvement. Firstly, a 1D numerical model with hierarchical 1D/3D approach based on GT-SUITE was developed and validated against the experimental data of engine torque and fuel consumption rate. This approach combined detailed analysis of in-cylinder flow, charge movement and combustion. Secondly, different intake strategies were designed and their effects on the intake mass flow rate and in-cylinder mass during the intake process, the swirl flow, tumble ratio and the turbulent kinetic energy during the compression process, the flame propagation and temperature distribution evolution after the spark ignition, and the pressure and heat release rate were numerically investigated. The results showed that compared with the original intake strategy, the asynchronized intake strategy (the intake valves close earlier and the intake valve lifts are reduced, while two intake valves have different intake strategy) reduces the backflow in the end of intake stroke, improves the in-cylinder swirl flow, increases the maximum heat release rate and shortens the combustion duration, and it is believed to be the optimized intake strategy. Finally, different cam profiles corresponding to the numerically designed intake strategies were applied to the bench test engine and the dyno experiments showed that the optimized intake strategy improves the torque and reduces the brake specific fuel consumption by 41.42% and 8.1% respectively at a low engine speed of 1200 rpm.

Suppression of super-knock in TC-GDI engine using two-stage injection in intake stroke (TSII)

Turbocharging and direct injection are main technologies used for energy-saving gasoline engines. But the biggest challenge is super-knock, whose mechanism is unclear and has no effective strategy to suppress this super-knock until now. The effects of injection strategies on super-knock were experimentally investigated in a turbocharged GDI engine. It was found that two-stage injections during intake stroke (TSII) can eliminate super-knock. Meanwhile, the fuel consumption, emissions and exhaust temperature can keep optimized level. By sweeping the start of the 1st injection (SOI1), end of the 2nd injection (EOI2) and the split injection ratios (ROI2) using 5000 cycles evaluation test at low-speed high load operating point, the optimized injection strategy for the typical TC-GDI engine is TSII with SOI1 at middle of intake stroke, EOI2 at end of intake stroke, and ROI2 of 0.3.

New evaluation index for bulk motion of in-cylinder flow through intake port system in cylinder head (II)

The variable intake systems recently tend to be adopted in gasoline engines for fuel economy and emission regulation. In the cases, because both swirl and tumble flows are together induced to the cylinder, in-cylinder flow pattern becomes very complicated so that we cannot decide this flow as one major pattern like swirl or tumble. The purpose of this study is to find new evaluation indexes for in-cylinder flow characteristics instead of a current swirl or a tumble ratio at the end of intake stroke using a steady flow test rig. To do this, port flow rig tests were conducted on the DOHC head varying lift of intake valves. Finally, the angular flow parameter PA and the flow angle (φ) were introduced as new evaluation indexes for in-cylinder angular flow characteristics at the end of intake stroke.

Measurement of Cycle-to-Cycle Variations and Cycle-Resolved Turbulencein an IC Engine Using a 3-D Particle Tracking Velocimetry.

Measurements of the instantaneous in-cylinder flow fields were carried out in a water analog engine simulation rig using a state of the art 3-D Particle Tracking Velocimetry(3-D PTV).Raw images for the 3-D PTV measurements were acquired at the end of intake stroke (Bottom Dead Center, BDC) for a simulated idle condition using a pair of high speed video cameras. Efforts were made to maximize the particle seeding density(and the resulting number of 3-D velocity vectors)to yield approximately 500 to 600 instantaneous vectors at each cycle. Using an appropriately designed spatial filter, large scale(low pass filtered) 3-D instantaneous velocity fields were reconstucted for each cycle as well as the ensemble averaged flow fields over large number of cycles. Based on these cycle-resolved(low pass filtered)flow fields and the ensemble averaged flow field, cycle-to-cycle variations were computed. Furthermore, the deviations of the instantaneous flow fields from the corresponding cycle-resolved large scale motions were computed to estimate the root mean square(rms)levels of the "in-cycle"turbulence. This paper presents the unique application of the 3-D PTV and the water analog engine simulation approach not only to measure the ensemble averaged mean 3-D flow patterns, but also to study the cycle-to-cycle stability of such flow patterns and ultimately to gain a better understanding of the combustion stability characteristics.

Effects of Operating Speed on 3-D Mean Flows Measured at the End of Intake Stroke in an IC Engine.

Measurements of the instantaneous in-cylinder flow fields at the end intake stroke at bottom dead center(BDC)were carried out in an FloDyneTM water analog engine simulation rig using 3-D particle tracking velocimetry(3-D PTV). The measurements were performed in a 4-valve per cylinder, typical pent-roof type combustion chamber with both intake valves activated generating mainly tumble vortex structures. The experiments were repeated for two different operating points simulating an idle condition(600 PRM)and a low load condition(1200 RPM). These two operating points represent almost a factor of two in effective Reynolds(Re)numbers. For each case, 100 cycles of data were acquired. Efforts were made to optimize the particle seeding density(and the resulting number of 3-D velocity vectors)to yield 500 to 600 instantaneous vectors at each cycle. The raw data coosisted of sets(between 50 000 and 60 000 velocity vectors each)of 3-D instantaneous(but phase conditioned at BDC)velocity vectors, randomly(but relatively uniformly)distributed over the entire cylinder volume. Sophisticated statistical tools were applied to these data sets to evaluate the ensemble averaged mean flow field and total fluctuation fields in the root mean square(r.m.s.)sense. In addition, "conventional" integral measures such as tumble, cross-tumble and swirl ratios were computed from the data by integrating the angular momentum components over the cylinder volume. The results indicate that the Re number effects are relatively small between the two conditions investigated, with a tendency of the smaller scale structures at BDC for the higher Re number case. This paper illustrates the tremendous potential of the water analog engine simulation used in conjunction with 3-D PTV as a rapid engine flow field evaluation tool. This approach allows to conveniently obtain 3-D maps of the mean and total r.m.s.fluctuation levels of each velocity components as well as integral parameters such as tumble and ratios(under realistic unsteady conditions). Furthermore, this method also allows various configurations or operating points to be conveniently compared with respect to many of their flow characteristics.