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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.

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.

Novel Diesel combustion concepts such as premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) promise lower NOx and PM emissions than those of conventional Diesel combustion. RCCI, which can be implemented using low-reactivity fuels such as gasoline or gases and high-reactivity fuels such as Diesel, has the potential to achieve extremely low emissions and improved thermal efficiency. However, to achieve RCCI combustion, a higher boost pressure than that of a conventional engine is required because a high EGR rate and a lean mixture are necessary to achieve a low combustion temperature. However, higher boost pressures can cause damage to intake systems. In this research, the addition of gaseous fuel to a CI engine is investigated to reduce engine emissions, mainly NOx and PM emissions, with the same IMEP level. Two different methods were evaluated.

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.

The combustion process using two fuels with different reactivity, known as dual-fuel combustion or RCCI is mainly studied to reduce emissions while maintaining thermal efficiency compared to the conventional diesel combustion. Many studies have proven that dual-fuel combustion has a positive prospect in future combustion to achieve ultra-low engine-out emissions with high indicated thermal efficiency. However, a limitation on high-load expansion due to the higher maximum in-cylinder pressure rise rate (mPRR) is a main problem. Thus, it is important to establish the operating strategy and study the effect of in-cylinder flow motion with dual-fuel combustion to achieve a low mPRR and emissions while maintaining high-efficiency. In this research, the characteristics of gasoline-diesel dual-fuel combustion on different hardware were studied to verify the effect of the in-cylinder flow motion on dual-fuel combustion.

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.

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.

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.

This paper provides an overview of spark-ignition engine unburned hydrocarbon emissions mechanisms, and then uses this framework to relate measured engine-out hydrocarbon emission levels to the processes within the engine from which they result. Typically, spark-ignition engine-out HC levels are 1.5 to 2 percent of the gasoline fuel flow into the engine; about half this amount is unburned fuel and half is partially reacted fuel components. The different mechanisms by which hydrocarbons in the gasoline escape burning during the normal engine combustion process are described and approximately quantified. The in-cylinder oxidation of these HC during the expansion and exhaust processes, the fraction which exit the cylinder, and the fraction oxidized in the exhaust port and manifold are also estimated.

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.

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.

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 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.

An LPG engine for heavy duty vehicles has been developed using liquid phase LPG injection (hereafter LPLI) system, which has regarded as as one of next generation LPG fuel supply systems. In this work the optimized piston cavities were investigated and chosen for an LPLI engine system. While the mass production of piston cavities is considered, three piston cavities were tested: Dog-dish type, bathtub type and top-land-cut bathtub type. From the experiments the bathtub type showed the extension of lean limit while achieving the stable combustion, compared to the dog-dish type at the same injection timing. Throughout CFD analysis, it was revealed that the extension of lean limit was due to an increase of turbulence intensity by the enlarged crevice area, and the enlargement of flame front surface owing to the shape of the bathtub piston cavity compared to that of the dog-dish type.

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.

Large-eddy simulation (LES) applications for internal combustion engine (ICE) flows are constantly growing due to the increase of computing resources and the availability of suitable CFD codes, methods and practices. The LES superior capability for modeling spatial and temporal evolution of turbulent flow structures with reference to RANS makes it a promising tool for describing, and possibly motivating, ICE cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Despite the growing interest towards LES in the academic community, applications to ICE flows are still limited. One of the reasons for such discrepancy is the uncertainty in the estimation of the LES computational cost. This in turn is mainly dependent on grid density, the CFD domain extent, the time step size and the overall number of cycles to be run. Grid density is directly linked to the possibility of reducing modeling assumptions for sub-grid scales.

Regulations regarding vehicles’ CO2 emissions are continuing to become stricter due to global warming. The CO2 regulations urge automobile manufacturers to develop gasoline engines with improved efficiency; however, the main obstacle to the improvement is the knock phenomenon in spark-ignition engines. If knock is predicted, the efficiency potential can be maximized in an engine by applying modest spark timing. Several research regarding knock prediction modeling have been conducted, and typically Livengood-Wu integral model is used to predict the knock occurrence. For the prediction, knock onset should be determined on a given pressure signal of given knock cycles for establishing the 0D ignition delay model. Several methodologies for knock onset determination have been developed because checking all the knock onset position by hand is impossible considering the breadth of data sets.

The increasing interest in the application of Large Eddy Simulation (LES) to Internal Combustion Engines (hereafter ICEs) flows is motivated by its capability to capture spatial and temporal evolution of turbulent flow structures. Furthermore, LES is universally recognized as capable of simulating highly unsteady and random phenomena driving cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Several quality criteria were proposed in the recent past to estimate LES uncertainty: however, definitive conclusions on LES quality criteria for ICEs are still far to be found. This paper describes the application of LES quality criteria to the TCC-III single-cylinder optical engine from University of Michigan and GM Global R&D; the analyses are carried out under motored condition.