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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.

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.

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.

The combustion and emission characteristics of a diesel engine running on butanol-diesel blends were investigated in this study. The blending ratio of n-butanol to diesel was varied from 0 to 40 vol% using an increment of 10 vol%, and each blend was tested on a 2.7 L V6 common rail direction injection diesel engine equipped with an EGR system. The test was carried out under two engine loads at a constant engine speed, using various combinations of EGR ratios and injection timings. Test results indicate that n-butanol addition to engine fuel is able to substantially decrease soot emission from raw exhaust gas, while the change in NOx emissions varies depending on the n-butanol content and engine operating conditions. Increasing EGR ratio and retarding injection timing are effective approaches to reduce NOx emissions from combustion of n-butanol-diesel blends.

Flash boiling spray is effective in improving the atomization and evaporation characteristics for gasoline direct injection engines. However, for a multi-hole injector the morphology structure of spray has an obvious change with the fuel temperature increasing or the ambient pressure decreasing, which influences the process of mixture formation and flame propagation. Specially, the spray collapses with both long penetration and a narrow spray angle above certain high superheat degree, which deteriorates air/fuel mixing and hence increases emissions. It is not desired for engine applications while the mechanism of spray structure transformation for multi-hole injector still remains unclear. In the present study, a systematic flash boiling spray model for multi-hole injector is built to investigate the flash boiling spray of multi-hole injector.

Chinese new legislations on two wheels and mopeds have been published recently. Depending on the latest exhaust statistic analyses, with the resulting of tighter limits, the application of catalytic converters is becoming a prevalent and a cost-efficient solution for Chinese motorcycle manufacturers. The phenomenon of exhaust temperature changes rapidly during real driving process is well known as one of major destructive factors which have effects upon converter's durability. One 125 cm3 motorcycle is selected as a typical model in this research project. Exhaust temperature of the 125 cm3 motorcycle is measured and recorded during the process of ECE 40 driving cycle. A simulation test system has been set up successfully depending on those temperature data. Conversion ratio of converter sample lost distinctly after 18 hours' thermal impact tests. After further analyses, there were not evident changes in microstructure and substance on the surface of converter.

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.

The combustion in low-speed two-stroke marine diesel engines can be characterized as large spatial and temporal scales combustion. One of the most effective measures to reduce NOx emissions is to reduce the local maximum combustion temperature. In the current study, multi-dimensional numerical simulations have been conducted to explore the potential of Miller cycle, high compression ratio coupled with EGR (Exhaust Gas Recirculation) and WEF (water emulsified fuel) to improve the trade-off relationship of NOx-ISFC (indicated specific fuel consumption) in a low-speed two-stroke marine engine. The results show that the EGR ratio could be reduced combined with WEF to meet the Tier III emission regulation. The penalty on fuel consumption with EGR and WEF could be offset by Miller cycle and high geometric compression ratio.

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.

For uniflow scavenged two-stroke marine diesel engines, the main function of scavenging process is to replace the burned gas with fresh charge. The end state of scavenging process is integral to the subsequent compression and combustion, thereby affecting the engine’s fuel economy, power output and emissions. In this paper, a complete working cycle of a large marine diesel engine was simulated by using the 3D-CFD software CONVERGE. The model was validated by mesh sensitivity test and experiment data. Based on this calibrated model, the influences of swirl ratio and exhaust valve closing (EVC) timing on the scavenging process were investigated. The parameters evaluating the performance of scavenging process were introduced. The results show that, by adjusting the swirl orientation angle(SOA) from SOA=10° to SOA=30°, different swirl ratios are generated and have obvious differences in flow characteristics and scavenging performance.

In-cylinder direct-injected technology provides a flexible and accurate optimization for internal combustion engines to reduce emission and improve fuel efficiency. With increasingly stringent requirements for the emissions of nitrogen oxides (NOx) and CO2, the content of injections in an engine combustion cycle has reached 7 to 9 times in gasoline direct injection (GDI) and the diesel engine with high-pressure common rail (HPCR). Accurate control of both time and quantity of injection is critical for engine performance and emissions, while the dynamic response of injector spray characteristics is a key factor. In this paper, a test bench was built for monitoring the dynamic response of solenoid injectors with high-speed micro-photography and synchronous current collection system. Experimental studies on the dynamic response of GDI and HPCR solenoid injectors were carried out.

Recent toxicological and epidemiologic studies have shown that diesel emissions have been a significant toxic air contaminant. Catalyzed DPF (CDPF) not only significantly reduces the PM mass emissions (>90%), but also further promotes carrier self-regeneration and oxidize more harmful gaseous pollutants by the catalyst coated on the carrier. However, some ultrafine particles and potentially harmful gaseous pollutants, such as VOCs species, originally emitted in the vapor-phase at high plume temperature, may penetrate through the CDPF filter. Furthermore, the components and content of catalyst coated on the CDPF could influence the physicochemical properties and toxicity intensity of those escaping ultrafine particles and gaseous pollutants. In this work, (1) we investigated the influence of precious metal content as a variable parameter on the physicochemical properties and catalytic activities of the small CDPF samples.

Particulate matter emissions have become a concern for the development of DISI engines. EGR has been extensively demonstrated as a beneficial technology to migrate knock performance, improve fuel economy and reduce NOX emissions. Recently, the effect of EGR on particulate matter emissions is attracting increased attention. This work investigates the effects of EGR on PN emissions with the variations of engine operating parameters and aims to understand the role of EGR in PN emissions for DISI engines. A 1.8liter turbocharged engine with cooled EGR is used for this study. The engine is operated at steady-state conditions with EGR under various operating parameters including injection timing, excess air ratio, and spark timing to characterize the particle number emissions. The results indicates that there is a high sensitivity of PN emissions to EGR with the variations of those parameters.

The evolution of surface functional groups (SFGs) and the graphitization degree of soot generated in premixed methane flames are studied and the correlation between them is discussed. Test soot samples were obtained from an optimized thermophoretic sampling system and probe sampling system. The SFGs of soot were determined by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) after removing the soluble impurities from the soot samples, while the graphitization degree of soot was characterized by Raman spectrum and electron energy loss spectroscopy (EELS). The results reveal that the number of aliphatic C-H groups and C=O groups shows an initial increase and then decrease in the sooting history. The large amount of aliphatic C-H groups and small amount of aromatic C-H groups in the early stage of the soot mass growth process indicate that aliphatic C-H groups make a major contribution to the early stage of soot mass growth.

Combustion control strategy for high efficiency and low emissions in a heavy duty (H D) diesel engine was investigated experimentally in a single cylinder test engine with a common rail fuel system, EGR (Exhaust Gas Recirculation) system, boost system and retarded intake valve closing timing actuator. For the operation loads of IMEPg (Gross Indicated Mean Effective Pressure) less than 1.1 MPa the low temperature combustion (LTC) with high rate of EGR was applied. The fuel injection modes of either single injection or multi-pulse injections, boost pressure and retarded intake valve closing timing (RIVCT) were also coupled with the engine operation condition loads for high efficiency and low emissions. A higher boost pressure played an important role in improving fuel efficiency and obtaining ultra-low soot and NOx emissions.

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.

Engine downsizing is one of the most effective means to improve the fuel economy of spark ignition (SI) gasoline engines because of lower pumping and friction losses. However, the occurrence of knocking combustion or even low-speed pre-ignition at high loads is a severe problem. One solution to significantly increase the upper load range of a 4-stroke gasoline engine is to use 2-stroke cycle due to the double firing frequency at the same engine speed. It was found that a 0.7 L two-cylinder 2-stroke poppet valve gasoline engine equipped with a two-stage serial boosting system, comprising a supercharger and a downstream turbocharger, could replace a 1.6 L naturally aspirated 4-stroke gasoline engine in our previous research, but its fuel economy was close to that of the 4-stroke engine at upper loads due to knocking combustion.

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.

Electrically assisted turbochargers are a promising technology for improving boost response of turbocharged engines. These systems include a turbocharger shaft mounted electric motor/generator. In the assist mode, electrical energy is applied to the turbocharger shaft via the motor function, while in the regenerative mode energy can be extracted from the shaft via the generator function, hence these systems are also referred to as regenerative electrically assisted turbochargers (REAT). REAT allows simultaneous improvement of boost response and fuel economy of boosted engines. This is achieved by optimally scheduling the electrical assist and regeneration actions. REAT also allows the exhaust turbine to operate within a narrow range of optimal vane positions relative to the unassisted variable geometry turbocharger (VGT). The ability to operate within a narrow range of VGT vane positions allows an opportunity for a more optimal turbine design for a REAT system.