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Engine knock is a major challenge that limits the achievement of higher engine efficiency by increasing the compression ratio of the engine. To address this issue, using a higher octane number fuel can be a potential solution to reduce or eliminate the propensity for knock and so obtain better engine performance. Methanol, a promising alternative fuel, can be produced from conventional and non-conventional energy resources, which can help reduce pollutant emissions. Methanol has a higher octane number than typically gasolines, which makes it a viable option for reducing knock intensity. This study compared the combustion characteristics of gasoline and methanol fuels in an optical spark-ignition engine using multiple spark plugs. The experiment was carried out on a single-cylinder four-stroke optical engine. The researchers used a customized metal liner with four circumferential spark plugs to generate multiple flame kernels inside the combustion chamber.

Pumping Mean Effective Pressure (PMEP) is the main factor limiting the improvement of thermal efficiency in a spark-ignition (SI) engine under low load. One of the ways to reduce the pumping loss under low load is to use Cylinder DeActivation (CDA). The CDA aims at reducing the firing density (FD) of the SI engine under low load operation and increasing the mass of air-fuel mixture within one cycle in one cylinder to reduce the throttling effect and further reducing the PMEP. The multi-stroke cycles can also reduce the firing density of the SI engine after some certain reasonable design, which is feasible to improve the thermal efficiency of the engine under low load in theory. The research was carried out on a calibrated four-cylinder SI engine simulation platform. The thermal efficiency improvements of the 6-stroke cycle and 8-stroke cycle to the engine performance were studied compared with the traditional 4-stroke cycle under low load conditions.

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.

A feasible method was developed to reconstruct the three-dimensional flame surface of SI combustion based on 2D images. A double-window constant volume vessel was designed to simultaneously obtain the side and bottom images of the flame. The flame front was reconstructed based on 2D images with a slicing model, in which the flame characteristics were derived by slicing flame contour modeling and flame-piston collision area analysis. The flame irregularity and anisotropy were also analyzed. Two different principles were used to build the slicing model, the ellipse hypothesis modeling and deep learning modeling, in which the ellipse hypothesis modeling was applied to reconstruct the flame in the optical SI engine. And the reconstruction results were analyzed and discussed. The reconstruction results show that part of the wrinkled and folded structure of the flame front in SI engines can be revealed based on the bottom view image.

The increasingly stringent requirements in relation to emission reduction and onboard diagnostics are pushing the Chinese automotive industry toward more innovative solutions and a rapid increase in electronic control performance. To manage the system complexity the architecture will require being well structure on hardware and software level. The paper introduces GEMS-K1 (Gasoline Engine Management System - Kit 1). GEMS-K1 is a platform being compliant with Euro IV emission regulation for gasoline engines. The application software is developed using modeling language, the code is automatically generated from the model. The driver software has a well defined structure including microcontroller abstraction layer and ECU abstraction layer. The hardware is following design rules to be robust, 100% testable and easy to manufacture. The electronic components use the latest innovation in terms of architecture and technologies.

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.

Strategies to suppress knock have been extensively investigated to pursue thermal efficiency limits in downsized engines with a direct-injection spark ignition. Comprehensive considerations were given in this work, including the effects of second injection timing and injector location on knock combustion in a downsized gasoline engine by large eddy simulation. The turbulent flame propagation is determined by an improved G-equation turbulent combustion model, and the detailed chemistry mechanism of a primary reference fuel is employed to observe the detailed reaction process in the end-gas auto-ignition process. The conclusions were obtained by comparing the data to the baseline single-injection case with moderate knock intensity. Results reveal that for both arrangements of injectors, turbulence intensity is improved as the injecting timing is retarded, increasing the flame propagation speed.

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.

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.

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.

Controlled Auto-Ignition (CAI) combustion can effectively improve the thermal efficiency of conventional spark ignition (SI) gasoline engines, due to shortened combustion processes caused by multi-point auto-ignition. However, its commercial application is limited by the difficulties in controlling ignition timing and violent heat release process at high loads. Stratified flame ignited (SFI) hybrid combustion, a concept in which rich mixture around spark plug is consumed by flame propagation after spark ignition and the unburned lean mixture closing to cylinder wall auto-ignites in the increasing in-cylinder temperature during flame propagation, was proposed to overcome these challenges.

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.

In order to achieve high-efficiency and clean combustion in HCCI engines, combustion must be controlled reasonably. A great variety of species with various reactivities can be produced through low temperature oxidation of fuels, which offers possible solutions to the problem of controlling in-cylinder mixture reactivity to accommodate changes in the operating conditions. In this work, in-cylinder combustion characteristics with low temperature reforming (LTR) were investigated in an optical engine fueled with low octane number fuel. LTR was achieved through low temperature oxidation of fuels in a reformer (flow reactor), and then LTR products (oxidation products) were fed into the engine to alter the charge reactivity. Primary Reference Fuels (blended fuel of n-heptane and iso-octane, PRFs) are often used to investigate the effects of octane number on combustion characteristics in engines.

Turbulent jet ignition (TJI) has the advantages of improving burning rates and expanding lean burn limitations of gasoline engines. Based on a single cylinder engine, combustion process with different ignition methods, including single spark ignition, twin spark ignition, one-hole TJI and seven-hole TJI, are studied in this work. Experiments are carried out under conditions with different air/fuel equivalence ratios and different engine loads. Results show that the cycle-to-cycle variations of TJI combustion, which is evaluated by coefficient of variations (CoV) of IMEP and CoV of peak pressure, are obviously reduced due to the fast burning rate induced by the jet flame, and one-hole TJI combustion has the best combustion stability, especially for reducing the CoV of peak pressure.

Controlled Auto-Ignition (CAI), also known as Homogeneous charge compression ignition (HCCI), has been the subject of extensive research because of their ability to providing simultaneous reduction in fuel consumption and NOx emissions in a gasoline engine. However, due to its limited operation range, combustion mode switching between CAI and spark ignition (SI) combustion is essential to cover the overall operational range of a gasoline engine for passenger car applications. Previous research has shown that the SI-CAI hybrid combustion has the potential to control the ignition timing and heat release process during both steady state and transient operations. However, it was found that the SI-CAI hybrid combustion process is often characterized with large cycle-to-cycle variations, due to the flame instability at high dilution conditions.

Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions.

Engine knock is an abnormal phenomenon, which places barriers for modern Spark-Ignition (SI) engines to achieve higher thermal efficiency and better performance. In order to trigger more controllable knock events for study while keeping the knock intensity at restricted range, various spark strategies (e.g. spark timing, spark number, spark location) are applied to investigate on their influences on knock combustion characteristics and pressure oscillations. The experiment is implemented on a modified single cylinder Compression-Ignition (CI) engine operated at SI mode with port fuel injection (PFI). A specialized liner with 4 side spark plugs and 4 pressure sensors is used to generate various flame propagation processes, which leads to different auto-ignition onsets and knock development. Based on multiple channels of pressure signals, a band-pass filter is applied to obtain the pressure oscillations with respect to different spark strategies.

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.

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.

Most of algorithms of lane detection mainly aim at the scenes of daytime. However, those algorithms are unstable for the lane detection at night because the camera is very sensitive to the light change. This paper proposed a lane detection algorithm that largely improves the detection system’s performance when it is used at night. The algorithm has two main stage: Image processing and Kalman filter (KF). The key process steps of Stage 1 are: extracting the Region of Interesting (ROI)→Edge Detection →Binarization→Hough→ Lane Selection→Lane fitting. First step, a ROI could be extracted according to the relatively fixed location of lanes. In step of edge detection, we use a creative filter named Correlation filter to remove image noise and remain the feature of lane. The filter matrix looks like “[0 1 1, −1 0 1; −1 −1 0]”. Next, the candidate lines are detected by the Hough transform, then, the equations of lane are acquired by fitting spots obtained from Hough.