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The fuel injection process in the port of a firing 4-valve SI engine at part load and 25°C head temperature was observed by a high speed video camera. Fuel was injected when the valve was closed. The reverse blow-down flow when the intake valve opens has been identified as an important factor in the mixture preparation process because it not only alters the thermal environment of the intake port, but also strip-atomizes the liquid film at the vicinity of the intake valve and carries the droplets away from the engine. In a series of “fuel-on” experiments, the fuel injected in the current cycle was observed to influence the fuel delivery to the engine in the subsequent cycles.

Currently, diesel engine-out exhaust NOx emission level prediction is a major challenge for complying with the stricter emission legislation and for control purpose of the after-treatment system. Most of the NOx prediction research is based on the Zeldovich thermal mechanism, which is reasonable from the physical point of view and for its simplicity. Nevertheless, there are some predictable range limitations, such as low temperature with high EGR rate operating conditions or high temperature with low EGR rates. In the present paper, 3 additional considerations, pilot burned gas mixing before the main injection; major NO formation area; concentration correction, were applied to the previously developed real-time NO estimation model based on in-cylinder pressure and data available from ECU. The model improvement was verified on a 1.6 liter EURO5 diesel engine in both steady and transient operation.

The measurement of spray penetration length is one of crucial tasks for understanding the characteristics of diesel spray and combustion. For this reason, many researchers have devised various measurement techniques, including Mie scattering, schlieren photography, and laser induced exciplex fluorescence (LIEF). However, the requirements of expensive lasers, complicated optics, delicate setups, and tracers that affect fuel characteristics have been disadvantages of previous techniques. In this study, the background-oriented schlieren (BOS) technique is employed to measure the vapor penetration length of diesel spray for the first time. The BOS technique has a number of benefits over the previous techniques because of its quantitative, non-intrusive nature which does not require lasers, mirrors, optical filters, or fuel tracers.

Ethanol, one of the most widely used biofuels, has the potential to increase the knock resistance of gasoline and decrease harmful emissions when blended with gasoline. However, due to the characteristics of ethanol, a trade-off relationship between knock tolerance and BSFC exists which is balanced by the blending ratio of gasoline and ethanol. Furthermore, in a spark-ignited engine, it is reported that the blending ratio that maximizes thermal efficiency varies based on the engine operating conditions. Therefore, an injection system that can deliver gasoline and ethanol separately is needed to fully exploit the benefit of ethanol. In this study, PFI injectors and a DI injector are used to deliver ethanol and gasoline, respectively. Using the dual fuel injection system, the compression ratio was increased from 9.5 to 13.3, and the knock mitigation characteristics at the full load condition were examined.

In an HSDI Diesel engine, fuel can be injected to the combustion chamber earlier as a strategy to reduce NOx and soot emissions. However, in the case of early injection the in-cylinder pressure and temperature during injection are much lower than those of normal injection conditions. As a result, wall impingement can occur if the conventional spray angle and piston bowl shape are maintained. In this study, 3-D CFD simulation was used to modify the spray angle of the injector and the piston bowl shape so that wall impingement was minimized, and soot emissions were reduced. The wall impingement model was used to simulate the behavior of impinged droplets. In order to predict the performance and emissions of the engine, a flamelet combustion model with the kinetic chemical mechanism for NOx and soot was used. A reduction in soot emissions was achieved with the modification of the spray angle and piston bowl shape.

To understand the effects of crevices on the engine-out hydrocarbon emissions, a series of engine experiments was carried out with different piston crevice volumes and with simulated head gasket crevices. The engine-out HC level was found to be modestly sensitive to the piston crevice size in both the warmed-up and the cold engines, but more sensitive to the crevice volume in the head gasket region. A substantial decrease in HC in the cold-to-warm-up engine transition was observed and is attributed mostly to the change in port oxidation.

The liquid fuel film on the cylinder liner is believed to be a major source of engine-out hydrocarbon emissions in SI engines, especially during cold start and warm-up period. Quantifying the liquid fuel film on the cylinder liner is essential to understand the engine-out hydrocarbon emissions formation in SI engines. In this research, two-dimensional visualization was carried out to quantify liquid fuel film on the quartz cylinder liner in an SI engine test rig. In addition, comparing visualization results with the trend of hydrocarbon emissions in this engine, the effect of cylinder wall-wetting during a simulated cold start and warmed-up condition was investigated with the engine experiment. The visualization was based on laser-induced fluorescence and total reflection. Using a quartz liner and a special lens, only the liquid fuel on the liner was visualized.

Ethanol is becoming more popular as a fuel component for spark-ignited engines. Ethanol can be used either as an octane enhancer of low RON gasoline or splash-blended with gasoline if a single injector is used for fuel injection. If two separate injectors are used, it is possible to inject gasoline and ethanol separately and the addition of ethanol can be varied on demand. In this study, the effect of the ethanol injection strategy on knock suppression was observed using a single cylinder engine equipped with two port fuel injectors dedicated to each side of the intake port and one direct injector. If the fuel is injected to only one side of the intake port, it is possible to form a stratified charge. The experiment was conducted under a compression ratio of 12.2 for various injection strategies.

To meet the stringent emission regulations on diesel engines, engine-out emissions have been lowered by adapting new combustion concepts such as low-temperature combustion and after-treatment systems have also been used to reduce tailpipe emissions. To optimize the control of both in-cylinder combustion and the efficiency of an after treatment system to reduce NOx, the amount of real-time NOx emissions should be determined. Therefore, in previous studies, the authors developed a real-time NO estimation model based on the in-cylinder pressure and the data available from the ECU during engine operation. The model was evaluated by comparing its results with a CFD model, which agreed well. Then, the model was implemented on an embedded system which allows real-time applications, and was verified on a 2.2-liter diesel engine. The model showed good agreement with the experimental results at various steady-state conditions and simple transient conditions.

Much research has been devoted to reducing NOx and soot emissions simultaneously in diesel engines. The low temperature combustion (LTC) concept has the potential to reduce these emissions at the same time, but it has limitations to its commercialization. In-cylinder EGR stratification is another combustion concept meant to reduce both types of emissions simultaneously using non-uniform in-cylinder EGR gas distribution. The EGR stratification concept uses a locally high EGR region of the in-cylinder so that the emissions can be reduced without increasing the overall EGR rate. In this study, the EGR stratification concept was improved with a CFD-based analysis. First, a two-step piston was developed to maximize the stratified EGR effect. Then, the feasibility of combustion and emission control by stratified EGR was evaluated under cases of artificially distributed EGR stratification and conventional diesel engine conditions.

Due to the direct injection of fuel into a combustion chamber, particulate emission is a challenge in DISI engines. Specifically, a significant amount of particulate emission is produced under the cold start condition. In this research, the main interest was to investigate particulate emission characteristics under the catalyst heating condition because it is one of the significant particulate-emissionproducing stages under the cold start condition. A single-cylinder optically accessible engine was used to investigate the effect of injection strategies on particulate emission characteristics under the catalyst heating condition. The split injection strategy was applied during intake stroke with various injection pressures and injection timings. Using luminosity analysis of the soot radiation during combustion, the particulate formation characteristics of each injection strategy were studied. Moreover, the factors that affect PM formation were analyzed via fuel injection visualization.

In this study, a correlation between the maximum heat release rate and vibrations from a diesel engine block was derived, and a methodology to determine the maximum heat release rate is presented. To investigate and analyze the correlation, an engine test and an actual road vehicle test were performed using a 1.6-L diesel engine. By varying the engine speed, load and main injection timing, the vibration signals from the engine block were measured and analyzed using a continuous wavelet transform (CWT). The results show that the maximum heat release rate has a strong correlation with the magnitude of the vibrations. A specific bandwidth, the vibration signals between 0.3∼1.5 kHz, was affected by the variation in the heat release rate. The vibrations excited by combustion lasted over 50 CAD; however, the signals during the period of 35 CAD after the start of injection had a dominant effect on the maximum heat release rate.

A gasoline homogeneous charged compression ignition (HCCI) called the controlled auto ignition (CAI) engine is an alternative to conventional gasoline engines with higher efficiency and lower emission levels. However, noise and vibration are currently major problems in the CAI engine. The problems result from fast burning speeds during combustion, because in the CAI engine combustion is controlled by auto-ignition rather than the flame. Thus, the ignition delay of the local mixture has to vary according to the location in the combustion chamber to avoid noise and vibration. For making different ignition delays, stratification of temperature or mixing ratio was tested in this study. In charge stratification, which determines the difference between the start of combustion among charges with different properties, two kinds of mixtures with different properties flow into two intake ports.

In recent years, Large-Eddy Simulation (LES) is spotlighted as an engineering tool and severe research efforts are carried out on its applicability to Internal Combustion Engines (ICEs). However, there is a general lack of definitive conclusions on LES quality criteria for ICE. This paper focuses on the application of LES quality criteria to ICE and to their correlation, in order to draw a solid background on future LES quality assessments for ICE. In this paper, TCC-III single-cylinder optical engine from University of Michigan is investigated and the analysis is conducted under motored condition. LES quality is mainly affected by grid size and type, sub-grid scale (SGS) model, numeric schemes. In this study, the same grid size and type are used in order to focus on the effect on LES quality of SGS models and blending factors of numeric scheme only.

An experimental study was performed to evaluate the effects of ethanol blending on to gasoline spray and combustion characteristics in a spray-guided direct-injection spark-ignition engine under lean stratified operation. The spray characteristics, including local homogeneity and phase distribution, were investigated by the planar laser-induced fluorescence and the planar Mie scattering method in a constant volume chamber. Therefore, the single cylinder engine was operated with pure gasoline, 85 %vol, 50 %vol and 25vol % ethanol blended with gasoline (E85, E50, E25) to investigate the combustion and exhaust emission characteristics. Ethanol was identified to have the potential of generating a more appropriate spray for internal combustion due to a higher vapor pressure at high temperature conditions. The planar laser-induced fluorescence image demonstrated that ethanol spray has a faster diffusion velocity and an enhanced local homogeneity.

The effect of secondary air injection (SAI) on exhaust hydrocarbon (HC) emission has been investigated in a spark-ignition (SI) single cylinder engine operating at steady-state cold condition. Both continuous SAI and synchronized SAI, which corresponds to intermittent secondary air injection to exhaust port, are tested. Oxidation characteristics of HC are monitored with a FID analyzer and exhaust gas temperatures with thermocouples. Effects of exhaust air-fuel ratio (A/F), location of SAI, and engine-A/F have been investigated. Results show that HC reduction rate increases as the location of SAI is closer to the exhaust valve for both synchronized and continuous SAIs. HC emission decreases with increasing exhaust-A/F when exhaust-A/F is rich, and is relatively insensitive when exhaust-A/F is lean. In synchronized SAI, SAI timing has significant effect on HC reduction and exhaust gas temperature. Optimum SAI timing observed is ATDC 100° and 230°.

Homogeneous Charge Compression Ignition combustion engines could have a thermal efficiency as high as that of conventional compression-ignition engines and the production of low emissions of ultra-low oxides of NOx and PM. HCCI engines can operate on most alternative fuels, especially, dimethyl ether which has been tested as possible diesel fuel for its simultaneously reduced NOx and PM emissions. However, to adjust HCCI combustion to practical engines, the main problem about the HCCI engine must be solved; control of its ignition timing and burn rate over a range of engine speeds and loads. Detailed chemical kinetic modeling has been used to predict the combustion characteristics. But it is difficult to apply detailed chemical kinetic mechanism to simulate practical engines because of its high complexity coupled with multidimensional fluid dynamic models. Thus, reduced chemical kinetic modeling is desirable.

Conventional combustion models are suitable for predicting flame propagation for a wrinkled flamelet configuration. But they cannot predict the burned gas composition. This causes the overestimation of burned gas temperature and pressure. A modified method of combustion simulation was established to calculate the chemical composition and to investigate their ultimate fate in the burned gas region. In this work, the secondary products of combustion process, like CO and H2, were considered as well as the primary products like CO2 and H2O. A 3-dimensional CFD program was used to simulate the turbulent combustion and a zero dimensional equilibrium code was used to predict the chemical composition of burned gas. With this simple connection, more reasonable temperature and pressure approaching the real phenomena were predicted without additional time costs.

In recent years, emission regulations have been getting increasingly strict. In the development of engines that comply with these regulations, in-cylinder pressure plays a fundamental role, as it is necessary to analyze combustion characteristics and control combustion-related parameters. The analysis of in-cylinder pressure data enables the modelling of exhaust emissions in which characteristic temperature can be derived from the in-cylinder pressure, and the pressure can be used for other investigations, such as optimizing efficiency and emissions through controlling combustion. Therefore, a piezoelectric pressure sensor to measure in-cylinder pressure is an essential element in the engine research field. However, it is difficult to practice the installation of this pressure sensor on all engines and on-road vehicles owing to cost issues.

The flamelet model is a widely used combustion model that demonstrates a good prediction of non-premixed combustion. In this model, the chemical time scales are considered to be smaller compared to those of the turbulence, which allows the heat and mass transfer equation to be decoupled from the flow equation. However, the model's dependency on the mixture fraction limits the combustion analysis to a single injection. To overcome this limitation, a two dimensional flamelet model, which uses two mixture fraction variables, was introduced to represent the non-premixed combustion of multiple injections. However, the model's computational time drastically increased due to the expansion of the solution domain. Thus, a modified 2-D flamelet model was introduced to reduce the computational time of the two dimensional flamelet model.