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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.

In this work, the operating strategy for diesel injection methods and a way to control the exhaust gas recirculation (EGR) rate under dual-fuel PCCI combustion with an appropriate ratio of low-reactivity fuel (propane) to achieve high combustion stability and low emissions is introduced. The standards of combustion stability were carbon monoxide (CO) emissions below 5,000 ppm and a CoV of the indicated mean effective pressure (IMEP) below 5 %. Additionally, the NOx emissions was controlled to not exceed 50 ppm, which is the standard of conventional diesel combustion, and PM emissions was kept below 0.2 FSN, which is a tenth of the conventional diesel value without a diesel particulate filter (DPF). The operating condition was a low speed and load condition (1,500 rpm/ near gIMEP of 0.55 MPa).

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.

The More precise control of the multiple-injection is required in common-rail injection system of direct injection diesel engine to meet the low NOx emission and optimal PM filter system. The main parameter for obtaining the multiple-injections is the mechanism controlling the injector needle energizing and movement. In this study, a piezo-driven diesel injector, as a new method driven by piezoelectric energy, has been applied with a purpose to develop the analysis model of the piezo actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code and to evaluate the effect of this control capability on spray formation processes. Aimed at simulating the hydraulic behavior of the piezo-driven injector, the circuit model has been developed and verified by comparison with the experimental results.

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.

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.

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.

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.

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.

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 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.