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The exhaust aftertreatment strategy is one of the most fundamental aspects of spark ignition engine technologies. For various types of engines (e.g., carburetor engine, PFI engine and GDI engine), measuring, purifying, modeling, and control strategies regarding the exhaust aftertreatment systems vary significantly. The primary goal of exhaust aftetreatment systems is to reduce the exhaust emission levels of NOx, HC and CO as well as to lower combustion soot. In general, there is a tradeoff among different engine performance aspects. The exhaust catalytic systems, such as the three way catalyst (TWC) and lean NOx trap (LNT) converters, can be applied together with the development of other engine technologies (e.g., variable valve timing, cold start). With respect to engine soot, some advanced diagnosing techniques are essential to obtain thorough investigation of exhaust emission mechanisms.

Ensuring lower emissions and better economy (fuel economy and after-treatment economy) simultaneously is the pursuit of future engines. An EGR-LNT synergetic control system was applied to a modified lean-burn CA3GA2 gasoline engine. Results showed that the synergetic control system can achieve a better NOx reduction than sole EGR and sole LNT within a proper range of upstream EGR rate and without the penalty in fuel consumption. It also has the potential to save costly noble metals in LNT, but excessive or deficient upstream EGR would make the synergetic control system inefficiency. In order to guarantee the objectivity of the effect of EGR-LNT synergetic control system on NOx reduction, another modified lean-burn CA4GA5 gasoline engine was additionally tested.

Gasoline partially premixed combustion (PPC) is a potential combustion concept to achieve high engine efficiency as well as low NOx and soot emissions. But the in-cylinder process of PPC is not well understood. In the present study, the double injection strategy of PPC was investigated on a light-duty optical engine. The fuel/air mixing and combustion process of PPC was evaluated by fuel-tracer planar laser-induced fluorescence (PLIF) and high-speed natural luminosity imaging technique, respectively. Combustion emission spectra of typical double injection case were analyzed. The primary reference fuel, PRF70 (70% iso-octane and 30% n-heptane by volume) was chosen as the lower reactivity fuel like gasoline. Double injection strategies of different first fuel injection timing and mass ratio of the two fuel injections were comparatively studied.

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.

Investigations using supercritical spray platform,which allows gasoline at low sub-critical state,subcritical state and supercritical state respectively,were made to demonstrate the Subcritical/ Supercritical Spray Characteristics of a Multi-Hole Gasoline Direct Injector. The experimental results show that the spray pattern and spray characteristics (i.e. spray penetration distance,spray area and spray perimeter) varied greatly under different state. In subcritical state,the spray characteristics of gasoline is similar to the phenomenon of "flash bfueling",appearing spray entrainment and spray collapse,then spray penetration distance and area drop significantly.In supercritical state,the six-hole gasoline spray is composed by the thick-core region and the thin-diffusion region,and Mach disk is observed at the outlet of the nozzle,then spray penetration distance and area increases sharply.

Poppet-valve two-stroke gasoline engines can increase the specific power of their four-stroke counterparts with the same displacement and hence decrease fuel consumption. However, knock may occur at high loads. Therefore, the combustion with stratified lean mixture was proposed to decrease knock tendency and improve combustion stability in a poppet-valve two-stroke direct injection gasoline engine. The effect of intake pressure and split injection on fuel distribution, combustion and knock intensity in lean mixture conditions at high loads was simulated with a three-dimensional computational fluid dynamic software. Simulation results show that with the increase of intake pressure, the average fuel-air equivalent ratio in the cylinder decreases when the second injection ratio was fixed at 70% at a given amount of fuel in a cycle.

A two-dimensional mesoscopic approach has been developed to investigate the flow and soot loading in the micro-channels of diesel particulate filter. Soot particle size examined is in the range of 10 nm to 10 μm. The flow is solved by an incompressible lattice Boltzmann model and the transport of solid particle is described in a Lagrangian frame of reference by cell automation probabilistic model. The lattice Boltzmann-cell automation probabilistic model (LB-CA model) is validated with the results of previous studies. The heterogeneous porous wall of DPF is generated by quartet structure generation set (QSGS). The effects of porous wall on the pressure field and velocity field are investigated. The distribution and deposition of soot particles with different sizes in clean channels are simulated. The dynamic evolution of solid boundary in soot particle capture process is investigated and the effects of the deposited soot particles on flow field are evaluated.

Although diesel engines have higher output torque, lower fuel consumption, and lower HC pollutant emissions, larger amounts of NOx and PM are emitted, compared with equivalent gasoline engines. The diesel particulate filters (DPF) have proved one of the most promising aftertreatment technologies due to the more stringent particulate matters (PM) regulations. In this study, the computational fluid dynamics (CFD) model of DPF was built by utilizing AVL-Fire software code. The main objective of this paper was to investigate the pressure drop and soot regeneration characteristics of hexagonal and conventional square cell DPFs with various inlet mass flow rates, inlet temperatures, cell densities, soot loads and ash loads. Different cell geometry shapes of DPF were evaluated under various ash distribution types.

Although diesel engines offer higher thermal efficiency and lower fuel consumption, larger amounts of Particulate Matters (PM) are emitted in comparison with gasoline engines. The Diesel Particulate Filters (DPF) have proved one of the most promising technologies due to the “particle number” emissions regulations. In this study, the Computational Fluid Dynamics (CFD) multi-channel model of DPF was built properly by utilizing AVL-Fire software code to evaluate the pressure drop and soot accumulation characteristics of DPF. The main objective of this paper was to investigate the effects of soot (capacity and deposit forms) and ash (capacity and distribution factors) interaction on DPF pressure drop and soot accumulation, as well as the effects of DPF boundary conditions (inlet mass flow rate and inlet temperature) on pressure drop.

The main objective of this paper was to investigate the pressure drop characteristics of ACT (asymmetric cell technology) design filter with various inlet mass flow rates, soot loads and ash loads by utilizing 1-D computational Fluid Dynamics (CFD) method. The model was established by AVL Boost code. Different ratios of inlet to outlet channel width inside the DPF (Diesel Particulate Filter) were investigated to determine the optimal structure in practical applications, as well as the effect of soot and ash interaction on pressure loss. The results proved that pressure drop sensitivity of different inlet/outlet channel width ratios increases with the increased inlet mass flow rate and soot load. The pressure drop increases with the increased channel width ratio at the same mass flow rate. When there is little soot deposits inside DPF, the pressure drop increases with the bigger inlet.

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.

Ethanol-Gasoline was being promoted in China. Ethanol as substitute fuel could save such nature resource that cannot be regenerated. At the same time, oxygen additives also have potential dangerous, such as, poisonous organic compound. In this paper, a typical 125 mL four stroke single cylinder motorcycle was driven on chassis dynamometer at 5 different stable conditions which is specified in ECE 40 driving cycle. At each stably driving condition, raw gas from exhaust pipe was collected in corresponding bags respectively. Those samples were analyzed by means of gas chromatogram and mass spectrum analyzer (Agilent GC6890-MS5973). Poisonous ethanol compound such as benzene, toluene had been found in samples from ethanol blended fueled motorcycle exhausts and compared with samples from that of pure gasoline.

Nowadays the strong knocking combustion involving destructive pressure wave or shock wave has become the main bottleneck for highly boosted engines when pursuing high thermal efficiency. However, its fundamental mechanism is still not fully understood. In this study, synchronization measurements through simultaneous pressure acquisition and high-speed direct photography were performed to comparatively investigate the strong knocking combustion of iso-octane and propane in a rapid compression machine with flat piston design. The pressure characteristics and visualized images of autoignition and reaction wave propagation were compared, and the correlations between thermodynamic trajectories and mixture reactivity progress were analyzed. The results show that iso-octane behaves a greater propensity to strong knocking combustion than propane at similar target pressures.

In this study, the characteristics and the advantages on engine performance of the reformed molecule HCCI (RM-HCCI) combustion fueled with gasoline were investigated by exergy analysis. The processes of fuel reforming and the closed portion of the engine cycle were simulated integrated with chemical kinetics mechanism at varied compression ratio (CR) and constant speed conditions. Results showed the fuel reforming under high temperature and oxygen-free condition by the exhaust heat recovery and electric heating assistance could drive gasoline to transform to the small-molecule gas fuels, meanwhile enhanced the chemical exergy of the fuel. The reformed fuel contributed to extending ignition delay, so less dilution required in RM-HCCI engine when expanding high load compared with gasoline HCCI engine. Thus, RM-HCCI engine could achieve higher load than gasoline HCCI engine, with the improvements by 12%, 26%, and 31% at CR17, CR19, and CR21, respectively.

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.

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.

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.

This research was focused on the effect of pre-chamber ignition and compared the knock limit of normal spark ignition in the main chamber and pre-chamber jet ignition combustion in a spark ignition gasoline engine. Experiments were conducted in a single-cylinder engine with optical access. Engine was operated with stoichiometric air/fuel mixtures at 1200 rev/min and different inlet pressures of 1, 1.2, and 1.4 bar. No auxiliary fuel was injected into the pre-chamber when jet-ignition mode was used. The results show that significant knock limit extension can be realized with use of a pre-chamber ignition unit. The main differences in engine performance, heat release and combustion, knock resistance and flame propagation were compared between the pre-chamber ignition and conventional spark ignition in the main chamber by in-cylinder pressure measurements and high-speed flame chemiluminescence imaging.

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.