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Homogeneous charge compression ignition (HCCI) combined with high compression ratio is an effective way to improve engines’ thermal efficiency. However, the severe thermodynamic conditions at high load may induce knocking combustion thus damage the engine body. In this study, advanced compression ignition knocking characteristics were parametrically investigated through RCM experiments and simulation analysis. First, the knocking characteristics were optically investigated. The experimental results show that there even exists detonation when the knock occurs thus the combustion chamber is damaged. Considering both safety and costs, the effects of different initial conditions were numerically investigated and the results show that knocking characteristics is more related to initial pressure other than initial temperature. The initial pressure has a great influence on peak pressure and knock intensity while the initial temperature on knock onset.

Combustion closed-loop control is now being studied intensively for engineering applications to improve fuel economy. Currently, combustion closed-loop feedback control is usually based on the cylinder pressure signal, which is the most direct and exact signal that reflects engine working process. Although there were some relatively cheap types of in-cylinder pressure sensors, cylinder pressure sensors have not been widely applied because of their high price now. Moreover, the combustion analysis based on cylinder pressure imposes high requirements on the information acquisition capability of the current ECU, such as high acquisition and analog-digital conversion frequency and so on. For developing a low price and feasible technology, a new engine information feedback method based on model calculation and crank angular velocity measurement was proposed. A simplified combustion model was operated in ECU for the real-time calculation of cylinder pressure and combustion parameters.

Lean-burn combustion is an effective method for increasing the thermal efficiency of gasoline engines fueled with stoichiometric fuel-air mixture, but leads to an unacceptable level of high cyclic variability before reaching ultra-low nitrogen oxide (NOx) emissions emitted from conventional gasoline engines. Multi-point micro-flame ignited (MFI) hybrid combustion was proposed to overcome this problem, and can be can be grouped into double-peak type, ramp type and trapezoid type with very low frequency of appearance. This research investigates the micro-flame ignition stages of double-peak type and ramp type MFI combustion captured by high speed photography. The results show that large flame is formed by the fast propagation of multi-point flame occurring in the central zone of the cylinder in the double-peak type. However, the multiple flame sites occur around the cylinder, and then gradually propagate and form a large flame accelerated by the independent small flame in the ramp type.

In order to understand the spray impinging the lubricant oil on the piston or cylinder wall in GDI engine, the Laser Induced Fluorescence (LIF) method was used to observe the phenomenon of the fuel droplets impact oil film and distinguish the fuel and oil during the impingement. The experimental results show that the hydrodynamic characteristics of impingement affected by the oil viscosity, droplets’ Weber number, oil film thickness. Crown formed after impingement. The morphology after impingement was categorized into: rings, stable crown, splash and prompt splash. Low oil film dynamic viscosity, high Weber number or thin oil film can facilitate splash. Splash droplets consist of fuel and oil, and the oil is the main component of splash droplets and crown. The empirical formula of critical We number (We) is fitted. High dimensionless oil film thickness or low oil film dynamic viscosity can increase the proportion of fuel in the crown.

Although supercharged system has been widely employed in downsized engines, the effect of supercharging on the intake flow characteristics remains inadequately understood. Therefore, it is worthwhile to investigate intake flow characteristics under high intake pressure. In this study, the supercharged intake flow is studied by experiment using steady flow test bench with supercharged system and transient flow simulation. For the steady flow condition, gas compressibility effect is found to significantly affect the flow coefficient (Cf), as Cf decreases with increasing intake pressure drop, if the compressibility effect is neglected in calculation by the typical evaluation method; while Cf has no significant change if the compressibility effect is included. Compared with the two methods, the deviation of the theoretical intake velocity and the density of the intake flow is the reason for Cf calculation error.

Noise source identification and separation of internal combustion engines is an effective tool for engine NVH (noise, vibration and harshness) development. Among various experimental approaches, noise source identification using signal processing has attracted extensive attention because of that the signal can be easily acquired and the requirements for equipment is relatively low. In this paper, variational mode decomposition (VMD) combined with independent component analysis (ICA) is used for noise source identification of a turbo-charged gasoline engine. Existing algorithms have been proved to be effective to extract signal features but also have disadvantages. One of the key problems in presently used method is that the main components of the signal, i.e. the main source of the noise, are unknown in advance. Thus the parameters selection of signal processing algorithms, which has a significance influence on the identification result, has no uniform criterion.

Two-stroke engines have to face the problems of insufficient charge for short intake time and the loss of intake air caused by long valve overlap. In order to promote the power of a two-stroke poppet valve diesel engine, measures are taken to help optimize intake port structure. In this work, the scavenging and combustion processes of three common types of intake ports including horizontal intake port (HIP), combined swirl intake port (CSIP) and reversed tumble intake port (RTIP) were studied and their characteristics are summarized based on three-dimensional simulation. Results show that the RTIP has better performance in scavenging process for larger intake air trapped in the cylinder. Its scavenging efficiency reaches 84.7%, which is 1.7% higher than the HIP and the trapping ratio of the RTIP reaches 72.3% due to less short-circuiting loss, 11.2% higher than the HIP.

A power nozzle is a fuel injection actuator in which fuel is instantly compressed and then discharged by a solenoid piston pump with nozzle. Fuel vaporization inside the power nozzles is a challenging issue. This paper presents an effective solution to the fuel vaporization problem in the power nozzle. An applied physical process, fluid boundary layer pumping (FBLP), is found in this study. FBLP can result in fuel circulation within the fuel line of the power nozzle, which on one hand brings heat out of the power nozzle, and on the other hand blocks vapor from entering the piston pump.

Due to the mechanical forces under static conditions, the engine cylinders cross section will not be a round circle any more once they are installed. The deformation of an engine cylinder causes increasing lubricating oil consumption and abnormal wear, resulting in worse fuel economy and emissions. However, prediction of deformation on a liner has not been made because of the complication of conditions and structure. In this study, a V6-type engine body model was built and meshed with Hypermesh suit software. Then, cylinder deformation under static condition has been simulated and analyzed. First of all, experimental work was done to verify the engine model. Basically, few parameters like pre-tightened force, structure and distribution of bolts have been investigated to figure out how the cylinder bore deformation behaves via finite element analysis. Also, a simple Matlab program was developed to process the data.

Wall temperature in GDI engine is influenced by both water jacket and gas heat source. In turn, wall temperature affects evaporation and mixing characteristics of impingement spray as well as combustion process and emissions. Therefore, in order to accurately simulate combustion process, accurate wall temperature is essential, which can be obtained by conjugate heat transfer (CHT) and piston heat transfer (PHT) models based on mapping combustion results. This CHT model considers temporal interaction between solid parts and cooling water. This paper presents an integrated methodology to reliably predict in-cylinder combustion process and temperature field of a 2.0L GDI engine which includes engine head/block/gasket and water jacket components. A two-way coupling numerical procedure on the basis of this integrated methodology is as follows.

In this work, both the ‘SCR-only’ and ‘EGR+SCR’ technical routes are compared and evaluated after the optimizations of both injection strategy and turbocharging system over the World Harmonized Stationary Cycle (WHSC) in a heavy duty diesel engine. The exhaust emissions and fuel economy performance of different turbocharging systems, including wastegate turbocharger (WGT), variable geometry turbocharger (VGT), two-stage fixed geometry turbocharger (WGT+FGT) and two-stage variable geometry turbocharger (VGT+FGT), are investigated over a wide EGR range. The NOx reduction methods and EGR introduction strategies for different turbocharger systems are proposed to improve the fuel economy. The requirement on turbocharging system and their potential to meet future stringent NOx and soot emission regulations are also discussed in this paper.

The main objective of this paper is to investigate the influence of injection pressures and fuel temperatures on the secondary injection spray evolution at the end of injection from a multi-hole gasoline direct injection (GDI) injector by Mie-scattering technique. The results of this paper show that the overall injection process can be classified into five stages which are injection delay stage, main injection stage, dwell stage, secondary injection stage and ligaments breakup stage respectively. Especially, the secondary injection occurs at the end of main injection, which is abnormal and undesirable spray behaviors. During the injection, big droplets and ligaments are injected through nozzle orifices at low speed. As the injection pressure increases, the phase of the secondary injection advances, and the injection duration decreases. At medium injection pressures (at 6, 8 MPa), more quantity of fuel are injected as ligaments.

In order to improve the combustion and emissions for high-speed marine diesel engines, numerical investigations on effects of different combustion chamber structures combined with intake air humidification have to be conducted. The study uses AVL Fire code to establish three-dimensional combustion model and simulate the in-cylinder flow, air-fuel mixing and combustion process with the flow dynamics metrics such as swirl number and uniformity index, analyze the interactional effects of combustion chamber structures and intake air humidification against the experimental data for a part load operation at 1350 r/min, find the optimized way to improve engine performance as well as decrease the NOx and soot emissions. The novelty is that this study is to combine different air humidifying rates with different combustion chamber structures including the re-entrant chamber, the straight chamber and the open chamber.

Butanol is a promising alcohol fuel. Previous studies on combustion and diesel engines showed different trends in sooting tendencies of the butanol isomers (n-butanol, iso-butanol, sec-butanol and tert-butanol).The impact of butanol isomers on the particulate emissions of GDI (Gasoline Direct Injection) engines, however, has not been reported. This work examines the combustion performance and particle number emissions of a GDI engine fueled with gasoline/butanol blends in steady state modes. Each isomer was tested at blend ratios from 10% to 50% by volume. Spark timings for all the fuels are set to obtain the maximum break torque (MBT), i.e. the MBT spark timings. Results show that the particle number concentration is reduced significantly with increasing butanol content for all the isomers.

On-board fuel reforming offers a prospective clean combustion mode for the engines. The flexible cylinder engine strategy (FCE) is a new kind of such mode. In this paper, the combustion of the primary reference fuel of PRF90 was theoretically investigated in a homogeneous charge compression ignition engine to validate the FCE mode, mainly focusing on the ignition delay time, the flame speed, and the emissions. The simulations were performed by using the CHEMKIN2.0 package to demonstrate the fuel reforming process in the flexible cylinder, the cooling effect on the reformed products, and the combustions of the mixture of the fresh fuel and the reformed products in the normal cylinders. It was found that the FCE mode decreased the ignition delay time of the fuel by about 35 crank angles at a typical engine condition.

In this paper, the influences of metallic content of lubricating oils on diesel particles were investigated. Three lubricating oils with different levels of metallic content were used in a 2.22 Liter, two cylinders, four stroke, and direct injection diesel engine. 4.0 wt. % and 8 wt. % antioxidant and corrosion inhibitor (T202) were added into baseline lubricating oil to improve the performance respectively. Primary particle diameter distributions and particle nanostructure were compared and analyzed by Transmission Electron Microscope. The graphitization degrees of diesel particles from different lubricating oils were analyzed by Raman spectroscopy. Conclusions drawn from the experiments indicate that the metallic content increases the primary particles diameter at 1600 rpm and 2200 rpm. The primary particles diameter ranges from 5 nm to 65 nm and the distribution conformed to Gaussian distribution.

Knock threshold detection is the key of closed loop control of ignition in gasoline engine, and it is also the difficult point in knock measurement. In this paper, an investigation of knock detection in turbocharged gasoline engine using bispectrum slice and ensemble empirical mode decomposition (EEMD) based on the engine cylinder head vibration signals is presented. By adding some finite amplitude Gaussian white noises to the signal, EEMD keeps the signal continuous in different time span, and therefore the mode mixing inhering in the classical empirical mode decomposition (EMD) method is alleviated. Power spectrum density (PSD) estimation is used to determine the band range of the resonance frequency generated by knock component. EEMD is used to decompose the original signals, the time-frequency characteristics of the Intrinsic Mode Functions (IMF) are analyzed using Continues Wavelet Transform (CWT) due to its excellent time-frequency resolution.

Matching fuel injection and airflow motion is critical for the optimization of fuel-air mixing and combustion process in diesel engines. In this study, the effects of swirl flow on liquid droplet motion and the selection of swirl ratio, which are known as the major concern in organizing airflow motion, were investigated based on theoretical analysis of droplet trajectories. The evaporating droplets with various initial conditions are assumed to be transported in a solid-body-like swirl field, and their trajectories were derived based on force analysis. To evaluate fuel-air mixing quality, a new parameter with respect to fuel vapor distribution was proposed. Based on this methodology, the effects of swirl velocity, droplet size, as well as liquid-gas density ratio on droplet trajectory were discussed under diesel-engine-like boundary conditions.

As the intake noise is a major contributing factor to automotive passenger compartment noise levels, it has received much more attention than before. Because the plastic manifolds could induce and transmit more noise owing to their lighter weight, aerodynamic noise has become a more serious problem in plastic manifolds than in conventional aluminum-made manifolds. Due to the complexity of aerodynamic noise of the intake system, it is difficult to predict the noise precisely, especially for the part whose frequency is higher than 1000 Hz. This paper introduces a new co-simulation method to simulate the aerodynamic noise at the engine inlet. With the coupled simulation between two programs, GT-Power and Fluent, it could simulate the gas flow inside the engine intake system, under the actual running condition of engine.

This paper investigated the effects of late intake valve closing timing (IVCT) and two-stage turbocharger systems matching based on partially premixed combustion strategy. Tests were performed on a 12-liter L6 heavy-duty engine at loads up to 10 bar BMEP at various speed. IVCT (where IVCT is -80°ATDC, -65°ATDC and -55°ATDC at 1300 rpm, 1600 rpm and 1900 rpm, respectively) lowered the intake and exhaust difference pressure, reducing pumping loss and improved the effective thermal efficiency by 1%, 1.5% and 2% at BMEP of 5 bar at 1300 rpm, 1600 rpm and 1900 rpm. For certain injection timings and EGR rate, it is found that a significant reduction in soot (above 30%) and NOx (above 70%) emissions by means of IVCT. This is due to that IVCT lowered effective compression ratio and temperature during the compression stroke, resulting in a longer ignition delay as the fuel mixed more homogeneous with the charge air ahead of ignition.