High Rail Pressure Research Articles

Experimental study on wall heat transfer from diesel spray flame in two-dimensional combustion chamber operated with rapid compression and expansion machine (RCEM)

Heat transfer phenomenon in internal combustion diesel engine is one of problems to be solved. This study was conducted to investigate the relationship between diesel spray impingement, combustion processes, and heat loss using a rapid compression and expansion machine (RCEM). Furthermore, spray combustion and heat transfer processes were investigated using multiple injection strategies with a 6-holes injector. The amounts of diesel fuel used in the pilot, pre-injection, and main injection sprays were 3.964, 0.747, and 11.205 mg, respectively. Variations in common rail pressure conditions (30, 120, and 180 MPa) were applied to properly investigate spray evaporation, air–fuel mixture formation, and heat transfer in the combustion chamber. In addition, a local wall heat flux sensor was installed in the cylinder (head and liner) and piston cavity (upper lip, lip, and bottom) to measure the heat flux distribution, and a diffused backlight illumination method was used to visualize the spray and flame behavior in the combustion chamber and 2D piston cavity. The results showed that the impingement flame surrounding the cylinder head contributed to the highest magnitude and longest duration of the heat flux on the cylinder side owing to the spray flame velocity, impingement, and residence time. Meanwhile, the highest different temperature at cavity bottom induced more heat flux on the cavity side than that on the squish side. In addition, the higher injection pressure increased the spray momentum and spray tip penetration which led to a better air–fuel mixture, better evaporation rate, and less flame residence that contributed to reduce the accumulated heat loss in combustion chamber. Furthermore, a low common rail pressure was found to induce a greater difference in the accumulated heat flux ratio than a high common rail pressure which is owing to longer flame residence time in the combustion chamber. They were approximately 14% and 6% greater than that compared to the baseline common rail pressure which mean that a high common rail pressure contributes for the improving thermal efficiency in spray combustion.

A parametric study to improve first firing cycle emissions of a gasoline direct injection engine during cold start

A parametric study was carried out for the first firing cycle of a 4-cylinder, 2.0-liter, turbocharged gasoline direct injection (GDI) engine. The primary goal was to see how changes in the fuel injection parameters would affect the GDI engine combustion and emissions for the first four combustion events that constitute the first firing cycle. Experimental studies were carried out with a custom-designed powertrain control system to measure the HC emissions and pressure development for the first firing cycle. The quantitative experimental results were accompanied by simulations of the detailed temporal and spatial fuel concentration profiles using Converge CFD engine simulation software. An alternative calculation method was used to calculate the average combustion equivalence ratio for each of the four cylinders. This method showed that the majority of the cold start HC emissions during the first firing cycle was unburned gasoline and its possible decomposition products, which did not contribute significantly to the combustion and heat release. For the same amount of fuel injected into a cylinder, increased fuel rail pressure resulted in better evaporation and combustion, while slightly increasing the HC emissions during the cold start process. A multiple injection strategy was studied that split the fuel delivery between the intake stroke and the compression stroke with either one or two injections in each of those strokes (two or four injections total). The quadruple injection strategy led to better first cycle combustion, with higher engine IMEP and lower HC emissions. This resulted from a richer fuel mixture in the region near the spark plug due to better fuel evaporation and a better spatial fuel distribution. While increasing fuel rail pressure with either injection strategy failed to significantly lower the HC emissions given the same amount of injected fuel mass, higher rail pressure with the quadruple injection strategy resulted in higher IMEP for the same amount of injected fuel; this may provide the possibility to reduce the total fuel injection mass which may have benefits for both fuel consumption and emissions.

DEVELOPING AND VALIDATING A GT-SUITE BASED MODEL FOR A SECOND GENERATION COMMONRAIL SOLENOID INJECTOR

Injection profiles, containing important parameters like injection rate, directly affect the spray structure, fuel-air mixture quality, and as such the physical and chemical processes occurring in the IC engine’s combustion chamber. Therefore, injection profiles are one of the keys to improving power, thermal efficiency and minimizing the emission for IC engines. In this paper, a GT-Suite - based simulation model for a second generation solenoid commonrail injector typically utilized in Hyundai 2.5 TCI-A diesel engines, has been successfully developed and validated. The validation is done by using experimental data are acquired by a Zeuch’s method-based Injection Analyzer (UniPg STS) in University of Perugia, Italy. The calibration data is measured over a wide range of rail pressure and energizing time (ET) corresponding to the engine operating conditions. The results show that the injector model developed here is reliable and suitable for examining the injector’s hydraulic characteristics. The difference in start of injection values obtained through experiment and simulation is only about 15 µs. The total injection volumes obtained through experiment and simulation under ET > 0.8 ms is less than 10 % while the difference is quite high under ET < 0.8 ms and high rail pressure (up to 34.5 %).

Microscopic study on the mechanisms for formation of the initial spray morphology

The initial spray morphology reflects the initial nozzle condition (quantity and distribution of residual fuel) derived from the previous injection, which will considerably affect the spray primary breakup. High-speed microscopic imaging technique and a single-hole diesel injector with a transparent Plexiglas nozzle were employed to investigate the mechanisms for the formation of initial spray tip morphologies and the corresponding breakup characteristics under various conditions. It was found that the interaction between liquid fuel and air bubbles, fuel properties and pressure shock-wave strength determined the spray tip morphology. Depending on the initial conditions, several types of morphologies were observed, namely, compact mushroom spray induced by surface tension under initial air-free condition, thin mushroom spray due to the acceleration effect of compressed air under low common rail pressure, drum spray tip (single or double drums) caused by the catastrophic breakup of air bubbles under common rail pressure, and mushroom-drum and central jet under fuel-free condition. Low common rail pressure allowed more time for the air bubbles to be compressed and more energy reserved in the compressed air, resulting in a higher possibility of mushroom spray formation through the accelerating effect. However, strong shock-wave under high pressure caused a high tendency for the catastrophic breakup of the air bubble and thereby production of the dispersed drum. In addition, less residual fuel left by the previous injection under high common rail pressure significantly suppressed the formation of mushroom tip.

Study on dynamic characteristics and control algorithm design for fuel metering valve of high-pressure pump

High rail pressure and multiple injections are crucial to improve diesel engine performance in terms of fuel efficiency and exhaust emission. As a drawback, rail pressure oscillations and complex pressure-wave propagation phenomena have impact on the control accuracy and response speed. Fuel metering valve, installed on the inlet of high-pressure pump, is the main mechanical actuator to adjust the rail pressure value. In this paper, the co-simulation model was established to investigate the dynamic process which is divided into three phases. The motion dead zones of the valve member and spring preload are the main factors for non-linearity working zone of the fuel metering valve. Therefore, the corresponding segmented control algorithm is designed to adjust the rail pressure based on the fuel flow rate and ideally realize synchronization of the control signals and rail pressure response.

Sensitivity analysis of the dynamic response of an electronic fuel injector regarding fuel properties and operating conditions

The sensitivity of fuel properties to the dynamic response (needle valve opening/closing delay and needle valve opening/closing time) of a electronic fuel injector was investigated. The fuel properties in different operating conditions were varied individually in bulk modulus, density and viscosity. Firstly, an electronic fuel injector model was built and validated by injection rate and injection mass at three different rail pressures and three different activation times. Secondly, a DOE (design of experiment) model was built and the Uniform Latin Hypercube (ULH) design method was applied to study the influences of the fuel properties on the injector dynamic response from a statistical point of view. The effects of the fuel properties were compared by using a SS-ANOVA (smoothing spline analysis of variance) method at both a low and a high rail pressure. The bulk modulus was found to play a dominant role in influencing the valve opening/closing delay at the low rail pressure. However, at the high rail pressure, the effects of the viscosity are prominent, while the effects of the bulk modulus and the density are negligible. Additionally, how these fuel properties affect the dynamic response were reported by RSM (Response Surface Method) function charts, and the details of the pressure differences and needle valve movements were also disclosed.

The Influence of Common-rail Adjustment on the Parameters of a Diesel Tractor Engine

The article deals with the issue of high-pressure indication of a diesel tractor engine Z 1727, which was fitted with a modern electronically controlled common-rail injection system. The aim of the study is to evaluate the influence of the adjustment of the fuel system – start of injection (SOI) timings and the rail pressure (PRAIL) – on the pressure development in the cylinder (PCYL), the heat release (HR) and the combustion noise level (CNLA). Furthermore, the article examines the influence of pilot and post fuel injections on the CNLA. The experiments were conducted at constant speed (1480 rpm) with four PRAILs and different SOI timings. As the results of measurements have shown, higher rail pressure causes higher pressure and a release of a larger amount of heat in the cylinder. These two parameters are the basic prerequisite for higher engine efficiency – higher power output of the engine at lower fuel consumption and decreased production of harmful emissions. Other advantages of the common-rail fuel system include the potential of dividing the main injection dose into the pilot injection and main injection, as well as the potential post injection. The measurements have further demonstrated that including a pilot injection phase significantly contributes to a decrease in combustion noise level as well as a more even, quieter operation of the engine.

Systematic LIF fuel wall film investigation

The combustion of gasoline in modern homogeneously operated DISI engines can result in soot particles and unburned hydrocarbons. One major source for these pollutants is the delayed evaporation of fuel wall films resulting from the impingement of the fuel spray onto cylinder walls or the piston, especially during warm-up when the walls have not yet reached operating temperatures and for early injection timings when the piston is still close to the injector. To reduce exhaust emissions and fuel consumption the behaviour of fuel films must be understood. This paper provides new findings of the influence of different boundary conditions on the wall film mass.In order to provide constant and defined boundary conditions, measurements were performed inside a pressure vessel. To reflect the wide range of operating conditions during the injection within an homogeneously charged engine, the vessel pressure, vessel temperature, rail pressure and distance between nozzle and wall were varied. The wall film patterns and masses were measured using the non-invasive method of laser-induced fluorescence. The spray was generated by a standard high-pressure, six-hole nozzle. Iso-octane was used as non-fluorescing surrogate fuel with 3-pentanone added as a well-characterised fluorescence tracer. It was found that with increasing surrounding temperature and increasing distance between nozzle and wall, the wall film mass decreases. Contrary to general assumptions, higher cylinder pressure, e.g. due to turbocharging, was found to increase fuel deposits. Higher rail pressures do not have a positive effect at low cylinder pressures but under turbocharged conditions the wall film mass can be reduced by increasing the rail pressure.

Influence of High Fuel Rail Pressure and Urea Selective Catalytic Reduction on PM Formation in an Off-Highway Heavy-Duty Diesel Engine

The influence of fuel rail pressure (FRP) and urea-selective catalytic reduction (SCR) on particulate matter (PM) formation is investigated in this paper along with notes regarding the NOx and other emissions. Increasing FRP was shown to reduce the overall soot and total PM mass for four operating conditions. These conditions included two high speed conditions (2400 rpm at 540 and 270 Nm of torque) and two moderated speed conditions (1400 rpm at 488 and 325 Nm). The concentrations of CO2 and NOx increased with fuel rail pressure and this is attributed to improved fuel-air mixing. Interestingly, the level of unburned hydrocarbons remained constant (or increased slightly) with increased FRP. PM concentration was measured using an AVL smoke meter and scanning mobility particle sizer (SMPS); and total PM was collected using standard gravimetric techniques. These results showed that the smoke number and particulate concentrations decrease with increasing FRP. However the decrease becomes more gradual as very high rail pressures. Additionally, the total PM decreased with increasing FRP; however, the soluble organic fraction (SOF) reaches a maximum after which it declines with higher rail pressure. The total PM was collected for the two 1400 rpm conditions downstream of the engine, diesel oxidationmore » catalyst, and a urea-SCR catalyst. The results show that significant PM reduction occurs in the SCR catalyst even during high rates of urea dosage. Analysis of the PM indicates that residual SOF is burned up in the SCR catalyst.« less