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Three-dimensional transient simulation was performed and an autoignition model was implemented to predict knock occurrence and autoignition site in a heavy-duty liquefied petroleum gas (LPG) engine. A flame area evolution (FAE) premixed combustion model was applied to simulate flame propagation. Engine experiments using a single-cylinder research engine were performed to calibrate the reduced kinetic model and to verify the result of this modeling. A pressure transducer and a head-gasket type ion-probe circuit board were installed to detect knock occurrence, flame arrival angle, and autoignition site. The simulation result shows good agreement with engine experiments. It also provides much information about in-cylinder phenomena and some ways to reduce knocking tendency. This knock simulation can be used as a development tool of engine design.

In this study, fundamental questions in improving thermal efficiency of spark-ignition engine were revisited, regarding two principal factors, that is, stroke-to-bore (S/B) ratio and valve timings. In our experiment, late intake valve closing (LIVC) camshaft and variable valve timing (VVT) module for valve timing control were equipped in the single-cylinder, direct-injection spark-ignition (DISI) engine with three different S/B ratios (1.00, 1.20, and 1.47). In these three setups, displacement volume and compression ratio (CR) were fixed. In addition, the tumble ratio for cylinder head was also kept the same to minimize the flow effect on the flame propagation caused by cylinder head while focusing on the sole effect of changing the S/B ratio.

CAI (Controlled Auto Ignition) combustion is already well known to be advantageous over conventional cycles in that it facilitates higher engine efficiency and has low emission characteristics. The CAI combustion process is mainly governed by in-cylinder RGF (Residual Gas Fraction), therefore achieving good control of in-cylinder RGF is essential in the development of CAI combustion engine. Usually, in-cylinder RGF controlled via low lift cam, short valve duration and negative valve overlap. More importantly on the other hand, accurate and instantaneous prediction of RGF must be done as a prerequisite to control. However, on-line prediction of RGF is not always practical due to the requirement of expensive fast response exhaust gas analyzers in the empirical case or otherwise due to theoretical models which are just too slow for application by means of simulation solving. In this paper, a newly enhanced theoretical model for predicting on-line in-cylinder RGF is introduced.

As global emission standards are becoming more stringent, it is necessary to increase thermal efficiency through the high compression ratio in spark-ignited engines. Various studies are being conducted to mitigate knocking caused by an increased compression ratio, which requires an understanding of the combustion phenomena inside the combustion chamber. In particular, the in-cylinder flow is a major factor affecting the entire combustion process from the generation to the propagation of flames. In the field of spark-ignited engine research, where interest in the concept of lean combustion and the expansion of the EGR supply is increasing, flow analysis is essential to ensure a rapid flame propagation speed and stable combustion process. In this study, the flow around the spark plug was measured by the Laser Doppler Velocimetry system, and the correlation with combustion in spark-ignited engines was analyzed.

This paper presents two closed-loop control methods for monitoring and improving the combustion behavior and the combustion noise on two 4-cylinder diesel engines, in which an in-cylinder pressure and an accelerometer transducer are used to monitor and control them. Combustion processes are developed to satisfy the stricter and stricter regulations on emissions and fuel consumption. These combustion processes are influenced by the factors such as engine durability, driving conditions, environmental influences and fuel properties. Combustion noise could be increased by these factors and is detrimental to interior sound quality. Therefore, it is necessary to develop robust combustion behaviors and combustion noise. For this situation, we have developed two closed-loop control methods. Firstly, a method using in-cylinder pressure data was developed for monitoring and improving the combustion noise of a 1.7L engine. A new index using the values calculated from the data was proposed.

The combustion noise of a diesel engine can be deteriorated by combustion characteristics such as the maximum rate of heat release and the start of combustion. These combustion characteristics in turn are influenced by the factors such as the engine NVH durability, driving conditions, environmental factors and fuel properties. Therefore, we need to develop the robust combustion noise that is insensitive to these factors. To achieve this aim, methods for predicting combustion characteristics has been developed by analyzing the vibration signal measured from the engine cylinder block. The closed-loop control of injection parameters through combustion characteristics prediction has been performed to produce the desired engine combustion performance. We constructed an ECU logic for the closed-loop control and verified the design in a diesel passenger car. We also evaluated the effect of combustion noise and fuel consumption by applying the closed-loop control.

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 work, the fuel film formation model was developed to investigate the distribution of wall fuel film on the cylinder wall of an SI engine. By integrating the continuity, momentum, and energy equations along the direction of fuel film thickness the simulation of the fuel film formation was carried out in the test rig. Spray impingement and fuel film models were incorporated into the computational fluid dynamics code, STAR-CD to calculate fuel film thickness and distribution of fuel film on the cylinder wall. With a laser-induced fluorescence method, the two-dimensional visualization of liquid fuel films was carried out to validate the simulation results.

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.

A reduced chemical kinetic mechanism for a gasoline surrogate was developed and validated in this study for CAI (Controlled Auto Ignition) combustion. The gasoline surrogate was modeled as a blend of iso-octane, n-heptane, and toluene. This reduced mechanism consisted of 44 species and 59 reactions, including main reaction paths of iso-octane, n-heptane, and toluene. The ignition delay times calculated from this mechanism showed a good agreement with previous experimental data from shock tube measurement. A rapid compression machine (RCM) was developed and used to measure the ignition delay times of gasoline and surrogate fuels in the temperature range of 890K ∼ 1000K. The RCM experimental results were also compared with the RCM simulation using the reduced mechanism. It was found that the chemical reaction started before the end of the compression process in the RCM experiment. And the ignition delay time of the suggested gasoline surrogate was similar to that of gasoline.

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.

As a result of stringent global regulations on fuel economy and CO2 emissions, the development of high-efficiency SI engines is more urgent now than ever before. Along with advanced techniques in friction reduction, many researchers endeavor to decrease the B/S (bore-to-stroke) ratio from 1.0 (square) to a certain value, which is expected to reduce the heat loss and enhance the burning rate of SI engines. In this study, the effects of B/S ratios were investigated in aspects of efficiency and knock characteristics using a single-cylinder LIVC (late intake valve closing) GDI (gasoline direct injection) engine. Three B/S ratios (0.68, 0.83 and 1.00) were tested under the same mechanical compression ratio of 12:1 and the same displacement volume of 0.5 L. The head tumble ratio was maintained at the same level to solely investigate the effects of geometrical changes caused by variations in the B/S ratio.

As the real-time supplying of hydrogen-rich gas becomes possible by the advances in the on-board fuel reforming technologies, utilizations of synthetic gas in IC engines are actively studied. However, due to the lack of fundamental studies on the combustion characteristics of synthetic gas, there is no precedent for the simulation of combustion process in synthetic gas fueled SI engine. In this study, the laminar flame speeds of synthetic gas and its mixture with iso-octane were calculated under extensive initial conditions of 3,575 points derived by combinations of temperature, pressure, fraction of lower heating value of synthetic gas and air-excess ratio variations.

The residual gas in SI engines is one of important factors on emission and performance such as combustion stability. With high residual gas fractions, flame speed and maximum combustion temperature are decreased and there are deeply related with combustion stability, especially at Idle and NOx emission at relatively high engine load. Therefore, there is a need to characterize the residual gas fraction as a function of the engine operating parameters. A model for predicting the residual gas fraction has been formulated in this paper. The model accounts for the contribution due to the back flow of exhaust gas to the cylinder during valve overlap and it includes in-cylinder pressure prediction model during valve overlap. The model is derived from the one dimension flow process during overlap period and a simple ideal cycle model.

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.

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.

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.