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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.

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 soot emission in direct-injection spark-ignition engines under various operating conditions was numerically investigated in the present study. A detailed soot model was used to resolve the physical soot process that consists of polycyclic aromatics hydrocarbon (PAH) formation and soot particle dynamics. The primary propagating flame in partially-premixed field was described by G-equation model, and the concentrations of burned species as well as PAH behind of the flame front were determined from the laminar flamelet library that incorporates the PAH chemical mechanism. The particle dynamics in post-flame region include nucleation, surface growth, coagulation, and oxidation were modeled by method of moments. To improve the model predictability, a gasoline surrogate model was proposed to match the real fuel properties, and the input of droplet size distribution of fuel spray was obtained from Phase-Doppler Particle Analyzer.

As EURO-6 regulations will be enforced in 2014, the reduction of NOx emission while maintaining low PM emission levels becomes an important topic in current diesel engine research. EGR is the most effective way to reduce the NOx emission because EGR has a dilution and thermal effect as a means to reduce the oxygen concentration and combustion temperature. Although EGR is useful in reducing the NOx emission, it suffers from a higher level of CO and THC emissions, which indicates a low combustion efficiency and poor fuel consumption. Therefore, in this research, a close post injection strategy, which is implemented using main injection and post injection, is introduced to improve combustion efficiency and to reduce PM emission under a high EGR rate. In addition, a modified hardware configuration using a double-row nozzle and a two-staged piston bowl geometry is adapted to improve the effect of the close post injection.

A waste heat recovery system is applied to a heavy-duty series hybrid electric vehicle. The engine in a series hybrid electric vehicle can operate at steady state for most of the time because the engine and drivetrain are decoupled, providing the waste heat recovery system with a steady state heat source. Thus, it is possible to optimize the waste heat recovery system design while maximizing the amount of useful energy converted in the system. To realize such a waste heat recovery system, the Rankine steam cycle is selected for the bottoming cycle. The heat exchanger is implemented as a quasi-1D simulation model to calculate the accurate quantity of recovered energy and to determine the working fluid state. The optimal geometric characteristics of the heat exchanger and the efficiency are considered according to the working fluid. The Rankine steam cycle model is constructed, and the output power is calculated.

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.

In compression ignition engines, the combustion starts after the ignition delay period from the start of injection. The degree of mixing between air and fuel during this period impacts combustion characteristics, such as the pressure rise rate, which worsens combustion noise. The formation of soot and nitrogen oxides can also be affected. In addition, ignition delay is essential to estimate the in-cylinder pressure. Therefore, there have been many researches performed to estimate the ignition delay for model-based control applications considering the above relations. In this study, a semiempirical and 0-dimensional ignition delay model is developed for real-time control applications. As the ignition delay consists of physical and chemical delays in compression ignition engines, the integrated ignition delay model considers both of these variables.

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.

Direct-injection spark-ignition (DISI) engines are regarded as a promising technology for the reduction of fuel consumption and improvement of engine thermal efficiency. However, due to direct injection, the shortened fuel-air mixing duration leads to a spatial gradient of the equivalence ratio, and these locally rich regions cause the formation of particulate matter. In the current study, numerical investigations on pollutant formation in a DISI engine were performed using combined flamelet models for premixed and diffusion flames. The G-equation model for partially premixed combustion was improved by incorporating the laminar flamelet library. Gasoline fuel was represented as a ternary mixture of gasoline surrogate and its laminar flame speeds were obtained under a wide range of engine operating conditions.

Various advanced combustion concepts, which can achieve higher thermal efficiency and emissions reduction, have been suggested as the emissions regulation gets stricter. Dual-fuel combustion that operates by using different fuels having both premixed and non-premixed combustion characteristics is one of the viable alternatives. In dual-fuel combustion, it is critical to understand air-fuel mixture distribution as it determines the ignition spot and following combustion phase. The fuel distribution in the engine is affected by various factors, such as chamber geometry, injection strategy or in-cylinder flow motion. Furthermore, among them, in-cylinder motion, usually described in terms of swirl or tumble motion, is mostly affected by in-cylinder port geometry. In this paper, 3-dimensional Computational Fluid Dynamics (CFD) was used to investigate the effect of in-cylinder flow motion in dual-fuel combustion. Two head and port geometries were used in the simulations.

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.

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.