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Improving fuel efficiency and emission characteristics are significant issues in engine research. Because the engine has complex systems and various operating parameters, the experimental research is limited by cost and time. One-dimensional (1D) simulation has attracted the attention of researchers because of its effectiveness and relatively high accuracy. In a 1D simulation, the applied model must be accurate for the reliability of the simulation results. Because in-cylinder turbulence mainly determines the combustion characteristics, and mean flow velocity affects the in-cylinder heat transfer and efficiency in a spark-ignited (SI) engine, a number of sophisticated models have been developed to predict in-cylinder turbulence and mean flow velocity. In particular, tumble is a significant factor of in-cylinder turbulence in SI engine.

The alternative fuel jet propellant 8 (JP-8, NATO F-34) can be used as an auto-ignition source instead of diesel. Because it has a higher volatility than diesel, it provides a better air-fuel premixing condition than a conventional diesel engine, which can be attributed to a reduction in particulate matter (PM). In homogeneous charged compression ignition (HCCI) or dual-fuel premixed charge compression ignition (PCCI) combustion or reactivity controlled compression ignition (RCCI), nitrogen oxides (NOx) can also be reduced by supplying external exhaust gas recirculation (EGR). In this research, the diesel and JP-8 injection strategies under conventional condition and dual-fuel PCCI combustion with and without external EGR was conducted. Two tests of dual-fuel (JP-8 and propane) PCCI were conducted at a low engine speed and load (1,500 rpm/IMEP 0.55 MPa). The first test was performed by advancing the main injection timing from BTDC 5 to 35 CA to obtain the emissions characteristics.

Increasing compression ratio is essential for developing future high-efficiency engines due to the intrinsic characteristics of spark-ignited engines. However, it also causes the unfavorable, abnormal knocking phenomena which is the auto-ignition in the unburned end-gas region. To cope with regulations, many researchers have been experimenting with various methods to suppress knock occurrence. In this paper, it is shown that cooling the combustion chamber using coolants, which is one of the most practical methods, has a strong effect on knock mitigation. Furthermore, the relationship between thermal boundary and coolant temperatures is shown. In the beginning of this paper, knock metrics using an in-cylinder pressure sensor are explained for readers, even though entire research studies cannot be listed due to the innumerableness. The coolant passages for the cylinder head and the liner were separated to examine independent cooling strategies.

CAI engine is well known to be advantageous over conventional SI engines because it facilitates higher engine efficiency and lower emission (NOx and smoke). However, its limited operation range, large cyclic variation, and difficulty in heat release control are still unresolved obstacles. Previous studies showed that a high load range of the CAI engine is limited mainly by the combustion noise caused by a stiff pressure rise (knock), and that a low load range is also limited by the combustion instability caused by the high dilution of residual gas. In this study, the characteristics of each cycle were analyzed to find the cause of the cycle variation at the high load limit of CAI operation. Moreover, to improve combustion stability, we tested the in-cylinder fuel stratification by applying nonsymmetrical fuel injection to the intake port. Experiments were performed on a PFI single cylinder research engine equipped with dual CVVT and low lift (2 mm) cam shaft with NVO strategy.

Emissions regulations are becoming more severe, and they remain a principal issue for vehicle manufacturers. Many engine subsystems and control technologies have been introduced to meet the demands of these regulations. For diesel engines, combustion control is one of the most effective approaches to reducing not only engine exhaust emissions but also cylinder-by-cylinder variation. However, the high cost of the pressure sensor and the complex engine head design for the extra equipment are stressful for the manufacturers. In this paper, a cylinder-pressure-based engine control logic is introduced for a multi-cylinder high speed direct injection (HSDI) diesel engine. The time for 50% of the mass fraction to burn (MFB50) and the IMEP are valuable for identifying combustion status. These two in-cylinder quantities are measured and applied to the engine control logic.

To properly respond to demands to reduce national energy consumption and meet greenhouse gas emission targets based on environment policy, the Ministry of Trade, Industry, and Energy of Korea formed a research consortium consisting of government agencies and academic and research institutions to establish the first fuel efficiency standards for medium- and heavy-duty (MHD) commercial vehicles. The standards are expected to be introduced in 2017 as Phase 1 of the plan and will regulate trucks with a gross vehicle weight in excess of 3.5 tons and buses with a carrying capacity of more than 16 persons. Most MHD commercial vehicles are custom-made and manufactured in diversified small-quantity batch production systems for commercial or public use, resulting in difficulties in utilizing mandatory vehicle tests for fuel efficiency evaluations.

Research on HEV (hybrid electric vehicle) intracity buses has become a topic of interest because the well-known service routes of intracity buses and the frequent stop/go pattern make the energy management of the vehicle straightforward. Thus, the energy flow and the energy management of the intracity bus have been studied extensively in order to improve fuel economy. However, the HEV buses that have been studied previously were equipped with a single traction motor or with dual motors with the same capacity for the convenience of the equipment without considering the motoring or generating efficiency of the traction motor. Therefore, the energy flow from the engine/generator unit to the traction motor that has been optimized by many kinds of energy distribution strategies could not be transferred to the wheels in the most efficient manner. This paper investigates this aspect of the energy flow.

Most research of internal combustion engine focuses on improving the fuel economy and reducing exhaust emissions to satisfy regulations and marketability. Engine combustion is a key factor in determining engine performance. Generally, engine operating parameters are optimized for the best performance and less exhaust emissions. However, abnormal combustion results in engine conditions that are far from an optimized operation. Abnormal combustion, including a misfire, can happen for a variety of reasons, such as superannuated vehicles, extreme changes in the driving environment, etc. Abnormal combustion causes serious deterioration of not only noise, vibration and harshness (NVH), but also the fuel economy and exhaust emission. NVH stands for unwanted noise, vibration and harshness from the vehicle. The misfiring especially deteriorates vehicle comfortability. Abnormal combustion at one cylinder breaks the exciting force balance between cylinders and causes unexpected vibration.

As emissions regulations become stricter, a variety of advanced combustion concepts that can reduce emissions with a higher thermal efficiency have been suggested. Dual-fuel combustion is one of the alternatives that has both premixed and non-premixed combustion characteristics. Knowing the effects of the mixture formation in dual-fuel combustion is important because it determines the ignition location and the following combustion phase. Hence, a thorough investigation on the related factors, such as the engine hardware or fuel spray, is required. Meanwhile, Computational Fluid Dynamics (CFD) is a good technique to visualize the in-cylinder phenomena and enables quantitative investigations into the detailed combustion characteristics. In this paper, a 3-dimensional CFD simulation was used to investigate the effects of the mixture formation in dual-fuel combustion. The combustion model consists of two parts.

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.

Since the amount of emitted CO2 is directly related to car fuel economy, attention is being drawn to DISI (Direct-Injection Spark-Ignition) engines, which have better fuel economy than conventional gasoline engines. However, it has been a problem that the rich air-fuel mixtures associated with fuel films during cold starts due to spray impingement produce particulate matter (PM). In predicting soot formation, it is important to predict the mixture field precisely. Thus, accurate spray and film models are a prerequisite of the soot model. The previous models were well matched with low-speed collision conditions, such as those of diesel engines, which have a relatively high ambient pressure and long traveling distances. Droplets colliding at low velocities have an order of magnitude of kinetic energy similar to that of the sum of the surface tension energy and the critical energy at which the splash occurs.

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°.

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.

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.

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.

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.

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.

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.

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.