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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.

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.

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.

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.

In order to improve the fuel consumption and expand the range of low fuel consumption area of a 1.5L Atkinson cycle PFI engine, the effect of the intake manifold length and chamber shape on the engine performance is investigated by setting up a GT-power (1-D) and an AVL-Fire (3-D) computational model which are calibrated with experimental data. After this the new engine was transformed to the test bench to do the calibration experiment. The results demonstrate that the intake manifold case_1 (the length is 300mm, side intake form) matched with a new designed chamber improves combustion in cylinder with a range 1.6∼7.4g/(kW•h) reduced in fuel consumption of speed that has been studied; the case_3 (the length is 100mm, intermediate intake form) matched with the new designed chamber with a range 3.86∼7g/(kW•h) reduced in fuel consumption of speed that has been studied. Both case_1 and case_3 expand the range of low fuel consumption area significantly.

This work numerically investigates the detailed combustion kinetics of partially premixed combustion (PPC) in a diesel engine under three different premixed ratio fuel conditions. A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict PPC combustion under various operating conditions. The experimental results showed that the increase of premixed ratio (PR) fuel resulted in advanced combustion phasing. To provide insight into the effects of PR on ignition delay time and key reaction pathways, a post-process tool was used. The ignition delay time is related to the formation of hydroxyl (OH). Thus, the validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how PR change the formation of OH during the low-to high-temperature reaction transition. The reaction pathway analyses of the formations of OH before ignition time were investigated.

The inverse boundary element method (IBEM) is presented to accurately identify the noise sources of a diesel engine in this study. The sound pressures on four near-field planes were measured as inputs for the method. Then, the acoustic model of the full diesel engine was established using the boundary element method, and the acoustic transfer vectors (ATV) between the surface normal velocity and acoustic pressure at field points were calculated over the frequency range of interest. Based on the measured sound pressure and the ATVs, the surface normal velocity distribution of the diesel engine was reconstructed by the IBEM. The reconstructed pressures at two reference field points were compared with the measured ones. Furthermore, the panel contribution of each engine component was analyzed through the reconstructed surface velocity.

Combustion cycle-to-cycle variation (CCV) of Spark-Ignition (SI) engines can be influenced by the cyclic variations in charge motion, trapped mass and mixture composition inside the cylinder. A high CCV leads to misfire or knock, limiting the engine’s operating regime. To understand the mechanism of the effect of flow field and mixture compositions on CCV, the present numerical work was performed in a single cylinder Direct Injection Spark-Ignition (DISI) engine. A large eddy simulation (LES) approach coupled with the G-equation combustion model was developed to capture the CCV by accurately resolving the turbulent flow field spatially and temporally. Further, the ignition process was modeled by sourcing energy during the breakdown and arc phases with a line-shape ignition model which could move with the local flow. Detailed chemistry was solved both inside and outside the flame front. A compact 48-species 152-reactions primary reference fuel (PRF) reduced mechanism was used.

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.

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.

Ammonia (NH3) is a carbon-free fuel, which could partially or completely eliminate hydrocarbon (HC) fuel demand. Using ammonia directly as a fuel has some challenges due to its low burning speed and low flammability range, which generates unstable combustion inside the combustion chamber. This study investigated the effect of two different compression ratios (CRs) of 10.5 and 12.5 on the performance of ammonia combustion by using a conventional single spark-ignition (SI) approach. It was found that at a lower CR of 10.5, the combustion was unstable even at advanced spark timing (ST) due to poor combustion characteristics of ammonia. However, increasing the CR to 12.5 improved the engine performance significantly with lower cyclic variations. In addition, this research work also observed the effect of multiple spark ignition strategies on pure ammonia combustion and compared it with the conventional SI approach for the same operating conditions.

Transparent materials such as Plexiglas and glass are applied in airplane and boat widely as the windows and hatches. There are three type stresses in the structure made of Plexiglas or glass, which are residual stresses from the casting, residual stresses due to manufacturing process involving sheet forming structure and the stresses from serving period. In the paper the stresses are studied by laser scattered Photoelasticy method. Phase shift method is presented to recognize scattered light patterns automatically. The residual stresses in Plexiglas plate and shell were analyzed by thin plate-shell theory. Stresses in the Plexiglas and shell were tested by laser scattered Photoelastic method.

Within a gasoline direct injection (GDI) engine, the impingement of fuel droplet on substrates induces various problems such as particular matter emission, oil dilution and abnormal combustion. Therefore, in order to solve these problems, it is urgent to have a clear understanding of the impingement behavior of fuel droplet impacting on substrates. Most previous studies have focused on the impingement of either water droplet on dry solid surface or the impinging droplet on the liquid film of the same type of liquid, while little research has been conducted on the impingement of fuel droplet on relevant substrates existing in GDI engines. The impingement of fuel droplet with higher Weber number on dry surface, fuel film and oil film with different thickness and viscosity were investigated experimentally. Results show that fuel droplet impacting on dry wall is easy to be deposited to form a fuel film. The fuel film attached to the wall is the main reason for the splash.

Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to improve gasoline engines’ efficiency and simultaneously achieve ultra-low NOx emissions. Two of the primary obstacles for applying CAI combustion are the control of combustion phasing and the maximum heat release rate. To solve these problems, dimethyl ether (DME) was directly injected into the cylinder to generate multi-point micro-flame through compression in order to manage the entire heat release of gasoline in the cylinder through port fuel injection, which is known as micro-flame ignited (MFI) hybrid combustion.

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.

Two identical helical ports and two identical directed ports were arranged into four different kinds of port combinations: helical and helical, helical and directed, directed and directed, directed and helical. Each port can rotate freely around its valve axis. The swirl ratio and the flow coefficient for each combination of intake ports were tested on a steady flow rig when both ports were positioned in different orientations around its valve axis. Two parameters, the loss rate of mean flow coefficient and the loss rate of angular momentum, were defined to describe the degree of interference between the flows discharging from the two adjacent intake valves. Velocity distribution in the vicinity and circumference of the intake valves was measured using Hot Wire Anemometer to further study the intake flow interference for different port combinations.

Proton exchange membrane (PEM) fuel cell is widely recognized as an outstanding portable power plant and expected to be possibly commercialization in the near future. As is well known, mechanical stresses implemented on the bipolar plates during the assembly procedure should have prominent influences on mass and heat transfer behavior inside the cell, as well as the resultant performance. In this study, an analytical model is proposed to comprehensively investigate the influence of clamping force on the mass transport, electrochemical properties and overall cell output capability of a PEM fuel cell. The results indicate that proper clamping force not only benefits the gas leakage prevention but also increases the contact area between the neighboring components to decrease the contact ohmic resistance.

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.

The effect of the Swirl Control Valve (SCV) on the in-cylinder flow characteristics was studied using LDA measurement in a single cylinder four-valve spark ignition engine with a SCV. Mean velocity, root-mean-square (rms) velocity fluctuation, and frequency structure of the velocity fluctuation were analyzed to illustrate flow features under the SCV open and closed conditions. The results show that when the SCV is open, large-scale flow structure in the cylinder is mainly tumble vortex, which will distort and break up during the late stage of the compression stroke. The rms velocity fluctuation increases during the compression process and reaches its maximum at certain crank angle before TDC. Larger scale eddies and lower frequency structures in the flow field become more near the end of compression process due to breakup of the tumble. The rms velocity fluctuation in the combustion chamber is roughly uniform at the end of the compression process.

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.