Kihyung Lee

Investigation of spray characteristics from a low-pressure common rail injector for use in a homogeneous charge compression ignition engine

Homogeneous charge compression ignition (HCCI) combustion provides extremely low levels of pollutant emissions, and thus is an attractive alternative for future IC engines. In order to achieve a uniform mixture distribution within the engine cylinder, the characteristics of the fuel spray play an important role in the HCCI engine concept. It is well known that high-pressure common rail injection systems, mainly used in diesel engines, achieve poor mixture formation because of the possibility of direct fuel impingement on the combustion chamber surfaces. This paper describes spray characteristics of a low-pressure common rail injector which is intended for use in an HCCI engine. Optical diagnostics including laser diffraction and phase Doppler methods, and high-speed camera photography, were applied to measure the spray drop diameter and to investigate the spray development process. The drop sizing results of the laser diffraction method were compared with those of a phase Doppler particle analyser (PDPA) to validate the accuracy of the experiments. In addition, the effect of fuel properties on the spray characteristics was investigated using n-heptane, Stoddard solvent (gasoline surrogate) and diesel fuel because HCCI combustion is sensitive to the fuel composition. The results show that the injector forms a hollow-cone sheet spray rather than a liquid jet, and the atomization efficiency is high (small droplets are produced). The droplet SMD ranged from 15 to 30 µm. The spray break-up characteristics were found to depend on the fuel properties. The break-up time for n-heptane is shorter and the drop SMD is smaller than that of Stoddard solvent and diesel fuel.

Turbulence and Cycle-by-Cycle Variation of Mean Velocity Generated by Swirl and Tumble Flow and Their Effects on Combustion

Combinations of swirl flow and tumble flow generated by 13 types of Swirl Control Valves were tested using both an impulse swirl meter and LDV. The LDV used in this study was developed especially for engine research to realize stable beam crossing at very narrow beam waists to achieve high spatial resolution measurement. It is shown that tumble flow generates turbulence in the combustion chamber more effectively than swirl flow, and that swirl reduces the cycle variation of mean velocity in the combustion chamber. Performance tests are also carried out to determine the combustion characteristics under the condition of homogeneous charge. Tumble flow promotes combustion to a greater extent than expected from its turbulence intensity. It is also shown that the lean-limit air/fuel ratio is not strongly related to cycle variation of mean velocity but to turbulence intensity.

Investigation of the spray characteristics for a secondary fuel injection nozzle using a digital image processing method

There are many ways to reduce diesel engine exhaust emissions. However, NOx emission is difficult to reduce because the hydrocarbon (HC) concentration in a diesel engine is not sufficient for NOx conversion. Therefore, in order to create stoichiometric conditions in the De-NOx catalyst, a secondary injection system is designed to inject liquid HC into the exhaust pipe. The atomization and distribution characteristics of the HC injected from a secondary injector are key technologies to obtain a high NOx conversion because inhomogeneous droplets of injected HC cause not only high fuel consumption but also deterioration of NOx emission. This paper describes the spray characteristics of a secondary injector including the spray angle, penetration length and breakup behaviour of the spray to optimize the reduction rate of the NOx catalyst. In this study, various optical diagnostics were applied to investigate these spray characteristics, the atomization mechanism and spray developing process. The visualization and image processing method for the spray pulsation were developed by high speed photography. The influence of the fuel supply pressure on the spray behaviour and a more detailed spray developing process have been analysed experimentally using image processing. Finally, the experimental results were used to correlate the spray structure to the injection system performance and to provide a design guide for a secondary injector nozzle.

Quantitative measurements of soot particles in a laminar diffusion flame using a LII/LIS technique

Methods to investigate soot formation are studied experimentally with a co-flow burner. In this study, the soot volume fraction, soot particle diameter and number density in a laminar diffusion flame are measured using LII/LIS (laser-induced incandescence/laser-induced scattering) techniques. For the purpose of quantification, validation tests needed to be conducted before the LII/LIS techniques were applied to measure soot formation, and the development of algorithm was also required to analyse the raw data. In the present study, extinction and scattering tests with a co-flow burner were performed to acquire calibration data. From these results, we decided the optimal laser beam intensity and obtained the LII signal from the diffusion flame. In addition, the algorithm for the LII/LIS simultaneous measurement was developed and applied to this algorithm to measure the soot volume fraction in the diffusion flame.

A study on the spray-wall interaction model considering degree of superheat in the wall surface

In this study, a new concept is proposed in order to simulate the behavior of a multi-component fuel spray impinging on a hot surface. The distillation curve of the fuel is considered so as to describe the vaporization property of each component in the gas oil, since the superheating degree of the surface, defined by the temperature difference between the wall surface and the fuel saturated temperature, affects the solid-liquid boiling state. First, some impinging sprays consisting of a single-component fuel are calculated to confirm the difference in vaporizing characteristics and impinging behavior in each fuel. Second, a spray impingement submodel is made. In this model, the difference of droplet breakup, reflection, and dispersion process with the difference of boiling state is considered based on several experimental results of impinging droplets on a hot wall. This new submodel is incorporated into KIVA-II code. The results calculated by this model are compared with those obtained by KIVA-II original code.In this study, a new concept is proposed in order to simulate the behavior of a multi-component fuel spray impinging on a hot surface. The distillation curve of the fuel is considered so as to describe the vaporization property of each component in the gas oil, since the superheating degree of the surface, defined by the temperature difference between the wall surface and the fuel saturated temperature, affects the solid-liquid boiling state. First, some impinging sprays consisting of a single-component fuel are calculated to confirm the difference in vaporizing characteristics and impinging behavior in each fuel. Second, a spray impingement submodel is made. In this model, the difference of droplet breakup, reflection, and dispersion process with the difference of boiling state is considered based on several experimental results of impinging droplets on a hot wall. This new submodel is incorporated into KIVA-II code. The results calculated by this model are compared with those obtained by KIVA-II origina...

A Study on the Characteristics of Spray and Combustion in a HCCI Engine according to Various Injection Angles and Timings

Premixed diesel engines have the potential to achieve a more homogeneous, leaner mixture near TDC compared to conventional diesel engines. Early studies have shown that the fuel injection timing and injection angle affect the mixture formation in a HCCI (Homogeneous Charge Compression Ignition) engine. Therefore in this study, we investigated the relationship between combustion and mixture formations accordance with injection conditions in a common rail direct injection type HCCI engine using an early injection strategy. From this results, we found that the fuel injection timing and injection angle affect the mixture formation and in turn affect combustion in the HCCI engine. In addition, this study revealed that the injection angle of 100° is effective to reduce smoke emission without any sacrificing power in the early injection case.

Effect of the heat exchanger in the waste heat recovery system on a gasoline engine performance

In this paper, the effects of increasing the back pressure on the engine performance by using heat exchangers mounted in the exhaust line to recover waste heat from the engine exhaust are described. An experimental study was conducted with two different types of heat exchanger, namely shell-and-tube-type heat exchangers and fin-and tube-type heat exchangers. The heat exchanger increased the resistance of the engine exhaust through the exhaust line, and the engine back pressure increased to 16 kPa, which led to an increase in the brake specific fuel consumption by up to 3% depending on the operating conditions. The back pressure adversely affected the performance of the automotive engine combined with the Rankine cycle and thus caused the overall thermal efficiency of the system to deteriorate. Consequently, if the back-pressure effect was taken into account, the contribution of recovering heat from the engine exhaust to the improvement in the system efficiency was lower than expected.

Application technique of particle image velocimetry and entropy analysis to investigate spray structure for gasoline direct injection injector

To improve the fuel consumption and exhaust emission for gasoline engines, the GDI (gasoline direct injection) system was spotlighted to meet these requirements. Many researchers have performed studies to investigate the spray characteristics and the mixture formation of the GDI injector. In this work, we studied the spray characteristics of a gasoline direct injector by using entropy analysis and particle image velocimetry (PIV) methods. The entropy analysis is based on the concept of statistical entropy, and it identifies the degree of homogeneity in the fuel concentration. The PIV algorithm was developed to elucidate the correlation between entropy and vorticity. From the applied results on a direct injection gasoline spray, we could find that the direct diffusion phenomenon was a dominant factor in the formation of a homogeneous mixture downstream of the GDI spray, especially under vaporizing ambient conditions, and the mixing phenomenon was also progressed by momentum exchange with induced air. In addition, these results revealed that entropy analysis and PIV are very effective methods for the analysis of the mixing process, and the entropy values increase with the progress of uniformity in the diffusion process.

Spray characteristics of four-hole injectors used for a hydrocarbon lean nitrogen oxide catalyst system in a diesel engine

Among emission reduction technologies, a hydrocarbon lean nitrogen oxide trap is a cost-effective solution for nitrogen oxide emission control in light-duty vehicles. However, the hydrocarbon lean nitrogen oxide trap leads to high fuel consumption because diesel fuel is normally used as a reducing agent (i.e. a reductant). It is necessary to establish injection conditions corresponding to the maximum nitrogen oxide conversion in the hydrocarbon lean nitrogen oxide trap system. A uniform distribution of the reducing agent is desirable, and the spray characteristics of the reductant, such as atomization and penetration, must be well understood in order to establish a good performance of the hydrocarbon lean nitrogen oxide trap. With this goal in mind, the spray characteristics and behaviour of a port fuel injector with four holes were analysed using visualization and r.m.s. image-processing techniques. The Sauter mean diameter distribution of the injector was measured using a Malvern system. The liquid agents employed in this study were ISO 4113 and n-heptane, which have properties similar to those of diesel and gasoline fuels respectively. These results elucidated the feasibility of a secondary injection system for the hydrocarbon lean nitrogen oxide trap.

The investigation of soot and temperature distributions in a visualized direct injection diesel engine using laser diagnostics

Based upon the method of temperature calibration using the diffusion flame, the temperature and soot concentrations of the turbulent flame in a visualized diesel engine were qualitatively measured. Two different cylinder heads were used to investigate the effect of swirl ratio within the combustion chamber. From this experiment, we find that the highest flame temperature of the non-swirl head engine is approximately 2400 K and that of the swirl head engine is 2100 K. In addition, as the pressure of fuel injection increases, the in-cylinder temperature increases due to the improved combustion of a diesel engine. This experiment represented the soot quantity in the KL factor and revealed that the KL factor was high when the fuel collided with the cylinder wall. Moreover, the KL factor was also high in the area of the chamber where the temperature dropped rapidly.