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The widespread application and increasingly stringent emission regulations call for more attention to optimize combustion process and emissions of marine diesel engine. This study conducts a numerical study to investigate the individual effect and their interaction of three post injection duration (3°CA, 5°CA and 7°CA), four spray included angles (145°, 150°, 155° and 160°) and four swirl ratios (0.5, 0.85, 1.2 and 1.6) in a marine diesel engine with main-post injection. These three parameters all exert impact on in-cylinder combustion performance and emissions by affecting fuel-air mixing quality. Results show that decreasing post injection duration from 7°CA to 3°CA shortens the combustion duration and decreases soot emission by 13.2%, while that induces a slight increase in NOx emissions by 1.0%. Spray included angle changes the spray targeting position within the combustion chamber.

An experimental study is carried out to investigate the coupling between dual loop EGR (DL-EGR) and variable geometry turbocharger (VGT) on a heavy-duty commercial diesel engine under different operating conditions and inlet conditions. The effects of VGT rack position and high-pressure (HP) proportion in DL-EGR on engine performance and emissions are studied. The boosting system is a series 2-stage turbocharger with a VGT as the HP-stage. The HP-Proportion in DL-EGR is swept from 0% to 100% while several intake pressure values and EGR rates are fixed by adjusting the VGT position. Results demonstrate that the VGT and HP EGR both have great influence on the exhaust enthalpy and turbocharger efficiency. The exhaust enthalpy and the intake demand have great influence on the DL-EGR split strategy.

Engine downsizing can effectively improve the fuel economy of spark ignition (SI) gasoline engines, but extreme downsizing is limited by knocking combustion and low-speed pre-ignition at higher loads. A 2-stroke SI engine can produce higher upper load compared to its naturally aspirated 4-stroke counterpart with the same displacement due to the double firing frequency at the same engine speed. To determine the potential of a downsized two-cylinder 2-stroke poppet valve SI gasoline engine with 0.7 L displacement in place of a naturally aspirated 1.6 L gasoline (NA4SG) engine, one-dimensional models for the 2-stroke gasoline engine with a single turbocharger and a two-stage supercharger-turbocharger boosting system were set up and validated by experimental results.

The fuel economy of plug-in hybrid electric city bus (PHEV) is deeply affected by driving cycle and travel distance. To improve the adaption of energy management strategy, the equivalent coefficient of fuel is the key parameter that needs to be pre-optimized based on the predicted driving cycle. An iterative learning method was proposed and implemented in order to get the best equivalent coefficient based on the predicted driving cycle and battery capacity. In the iterative learning method, the energy model and kinematics model of the bus were built. The ECMS (Equivalent Consumption Minimization Strategy) method was applied to obtain the best fuel economy with the given equivalent coefficient. The driving paths and running time of city buses were relatively fixed comparing with other vehicles, and their driving cycle can be predicted by route content. The proposed optimized strategy was applied on the factory sets of plug-in hybrid electric city bus.

Homogeneous charge compression ignition (HCCI) technology is promising to reduce engine exhaust emissions and fuel consumption in gasoline engine. However, it is still confronted with the problem of its limited operation range. High load is limited by the tradeoff between the quantity of working charge and dilution charge. Low load is limited by the high residual gas fraction and low temperature in the cylinder. One of the highlights of HCCI combustion research at present is to expand the low load limit of HCCI combustion by developing HCCI idle operation. The main obstacle in developing HCCI idle combustion is too high residual gas fraction and low temperature to misfire in cylinder. This paper relates to a method for achieving the appropriate environment for auto-ignition at idle and the optimal tradeoff between the combustion stability and fuel consumption by employing EIVO valve strategy with an equivalent air-fuel ratio.

This paper describes numerical simulations that compare the performance of two combustion CFD models against experimental data, and evaluates the effects of combustion and spray model constants on the predicted combustion and emissions under various operating conditions. The combustion models include a Characteristic Time Combustion (CTC) model and CHEMKIN with reduced chemistry models integrated in the KIVA-3Vr2 CFD code. The diesel spray process was modeled using an updated version of the KH-RT spray model that features a gas jet submodel to help reduce numerical grid dependencies, and the effects of both the spray and combustion model constants on combustion and emissions were evaluated. In addition, the performance of two soot models was compared, namely a two-step soot model, and a more detailed model that considers soot formation from PAH precursors.

Comparisons have been made between dual-fuel (80% port-injection gasoline and 20% direct-injection diesel by mass) Highly Premixed Charge Combustion (HPCC) and blended-fuel (80% gasoline and 20% diesel) Low Temperature Combustion (LTC) modes on a 1-L single-cylinder test engine. In the HPCC mode, both early-injection (E-HPCC) and late-injection (L-HPCC) of diesel have been used. The comparisons have been conducted with a fixed fuel injection rate of 50 mg/cycle at 1500 rpm, and with the combustion phasing fixed (by adjusting the injection timing) so that the 50% heat release point (CA50) is at 8° ATDC. The rapid heat release process of LTC leads to the highest maximum pressure rise rate (MPRR). A two-peak heat release process is observed in L-HPCC, resulting in a lower MPRR. The heat release rate and MPRR values for the E-HPCC are comparable to the L-HPCC values. The EHPCC mode provides the lowest NOX emission. The soot emissions for all three modes are low.

SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In order to investigate the effect of the thermal boundary condition on the hybrid combustion, the experiments with different coolant temperatures are performed to adjust the chamber wall temperature in a gasoline engine. The experimental results indicate that increasing wall temperature would advance the combustion phasing, enlarge the peak heat release rate and shorten the combustion duration. While the capacity of the wall temperature effect on the hybrid combustion characteristics are more notable in the auto-ignition dominated hybrid combustion.

In order to achieve high efficiency and clean combustion indiesel engines, many advanced combustion concepts have been developed to simultaneously reduce NOx and soot emissions with high efficiency. However, the benefits of these combustion modes are limited to low loads because the energy release ratesaretoo fast at high loads. Recently, Dual-fuel highly premixed charge combustion (HPCC) strategies with the port injection of gasoline and direct injection of diesel have demonstrated advantages in terms of extending the operating range by the flexible control of fuel chemical reactivity and charge stratification. However, the extension to high-load in a turbocharged multi-cylinder diesel engine with the HPCC is a critical challenge due to excessive pressure rise rates. Mean while it suffers from the excessive of CO/HC emissions at low loads.

This work concerns the oxidation of biodiesel surrogates in a CI engine. An experimental study has been carried out in a single-cylinder common-rail CI engine with soybean biodiesel and two biodiesel surrogates containing neat methyl decanoate and methyl decanoate/n-heptane blends. Tests have been conducted with various intake oxygen concentrations ranging from 21% to approximately 9% at intake temperatures of 25°C and 50°C. The results showed that the ignition delay and smoke emissions of neat methyl decanoate were closer to that of soybean biodiesel as compared with methyl decanoate/n-heptane blends. A reduced chemical kinetic mechanism for the oxidation of methyl decanoate has been developed and applied to model internal combustion engines. A KIVA code, coupled with the Chemkin chemistry solver, was used as the computational platforms. The effects of various intake oxygen concentrations on the in-cylinder emissions of OH and soot were discussed.

In this paper, the influences of lubricating base oils on diesel particles morphology and nanostructure were investigated. Four different lubricating base oils were blended in diesel at a mass ratio of 0.5% and 1.0% for combustion. Exhaust particle samples generated by a four-cylinder, four-stroke direct injection engine when employing neat diesel and four base oil dosed mixtures as the fuel were collected and compared. Primary particle diameter distributions and particle nanostructure were compared and analyzed by a High-Resolution Transmission Electron Microscope (HRTEM). Conclusions drawn from the experiments indicated that the primary particles diameter ranges from 5 nm to 70 nm and the distribution conformed to typical Gaussian distribution. Base oil II, III, IV increased the primary particles diameter, while particles from base oil I exhibited smaller size than that from neat diesel.

A bottoming waste-heat-recovery (WHR) model based on the Organic Rankine Cycle (ORC) is proposed to recover waste heat from exhaust gas and jacket water of a typical diesel engine (DE). The ORC model is detailed built based upon real structural and functional parameters of each component, and is able to precisely reflect the working process of the experimental ORC system constructed in lab. The DE is firstly tested to reveal its energy balance and the features of waste heat. The bottoming ORC is then simulated based on experimental data from the DE bench test using R245fa and R601a as working fluid. Thermodynamic evaluations are done on key parameters like waste heat recovered, expansion power, pump power loss and system efficiency. Results indicate that maximum expansion power and efficiency of the ORC are up to 18.8kW and 9.6%. Influences of engine condition, fluid mass flow and evaporating pressure on system performance are analyzed and meaningful regularities are revealed.

The effects of jet impingement and turbulence structure on jet mixing rate arc investigated by using a simultaneous measurement system of concentration and velocity. It is found that, after the end of injection, dispersion of momentum of a CO2 jet Is much faster than that of concentration. The residual gas is then left in a rather quiescent atmosphere, that makes a sluggish mixing process of the residual gas. Jet impingement can create intensive air motion in the near impingement region, that promotes the mixing of the residual gas. However, the effect of jet impingement decreases as the distance from the impingement point increases.

Although excellent progress has been made recently in powertrain fault diagnosis based on vibration signals, most of them are based on the assumption that the fault features of the training and test data are drawn from the same probability distribution. Due to the limitation of the domain shift phenomenon, the performance of the current intelligent fault diagnosis methods is significantly reduced. Even many existing transfer learning methods have the problem of low generalization ability. Inspired by sparse representation theory, a novel cross-domain fault diagnosis method based on K-means singular value decomposition (K-SVD) and long short-term memory network (LSTM) is proposed in this study. First, K-SVD can convert source domain data into a sparse dictionary and sparse coefficient. The domain-invariant features are explored in the sparse dictionary, which contains redundant features. The sparse coefficients are input into the LSTM to obtain a primary classifier.

To explore the exergy loss of engine combustion process, entropy generations were numerically analyzed through detailed chemical kinetics. It revealed that the reformed fuel with simpler molecular tended to produce lower combustion irreversibility. Furthermore, a promising high efficiency RM- HCCI (Reformed molecule HCCI) combustion principle was proposed. In a RM-HCCI engine, hydrocarbon fuels were reformed into small molecule fuels under high temperature and low/no oxygen atmosphere before injection into the cylinder when the exhaust gas enthalpy to a certain extent was recovered, further improving the engine efficiency. The second law efficiency (η2nd) of a RM-HCCI combustion with a CR of 10 can be increased from 36.78% to 45.47% by coordination of multiple control parameters, and to 67.79% by raising CR from 10 to 100.

An experimental study is carried out to compare the effects of high-pressure-loop, low-pressure-loop and dual-loop exhaust gas recirculation systems (HPL-EGR, LPL-EGR and DL-EGR) on the combustion characteristics, thermal efficiency and emissions of a diesel engine. The tests are conducted on a six-cylinder turbocharged heavy-duty diesel engine under various operating conditions. The low-pressure-loop portion (LPL-Portion) of DL-EGR is swept from 0% to 100% at several constant EGR rates, and the DL-EGR is optimized based on fuel efficiency. The results show that the LPL-EGR can attain the highest gross indicated thermal efficiency (ITEg) in the three EGR systems under all the tested conditions. At a middle load of 0.95 BMEP, 1660 r/min, the pumping losses of LPL-EGR lead to the lowest BTE among the EGR systems. The HPL-EGR can achieve the best brake thermal efficiency (BTE) and emissions within the EGR rate of 22.5% mainly due to the reduced pumping losses.