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Advanced combustion engines dominate all automotive applications. Future high efficiency clean combustion engines can contribute significantly to sustainable transportation. Effective ignition strategies are studied to enable lean and diluted combustion under considerably high-density mixture and strong turbulences, for improving the efficiency and emissions of future combustion engines. Continuous discharge and multi-site ignition strategies have been proved to be effective to stabilize the combustion process under lean and EGR diluted conditions. Continuous discharge strategy uses a traditional sparkplug with a single spark gap and multiple ignition coil packs. The ignition coil packs operate under a specific time offset to realize a continuous discharge process with a prolonged discharge duration. Multi-site ignition strategy also uses multiple ignition coil packs.

This empirical work investigates the impacts of thermodynamic parameters, such as pressure and temperature, and fuel properties, such as fuel Cetane number and aromatic contents on ignition delay in diesel engines. Systematic tests are conducted on a single-cylinder research engine to evaluate the ignition delay changes due to the fuel property differences at low, medium and high engine loads under different EGR dilution ratios. The test fuels offer a range of Cetane numbers from 28 to 54.2 and aromatic contents volume ratios from 19.4% to 46.6%. The experimental results of ignition delays are used to derive an ignition delay model modified from Arrhenius’ expression. Following the same format of Arrhenius’ equation, the model incorporates the pressure and temperature effects, and further includes the impacts of intake oxygen concentration, fuel Cetane number and aromatic contents volume ratio on the ignition delay.

As the invalidation of the oxygen sensor in the initial cycles at cold start, the engine can not operate based on the closed loop control based on oxygen sensor. And it may result in the misfire events and higher hydrocarbon (HC) emissions during this period. To solve this problem, a novel closed loop control based on ionization current in combustion cycle is proposed. The in-cylinder combustion quality is monitored by means of the ion current detection technique; meanwhile, if the misfire event is detected in the combustion cycle, the spark re-ignition is made in the current combustion cycle. In addition, to optimize the combustion and reduce HC emissions during cold start, the fuel injection quantity and ignition timing in the next cycle are adjusted based on the current ion current signal.

The effectiveness of after-treatment systems depends on the exhaust gas temperature, which is low during cold-start. As a result, Euro III, Euro IV and FTP75 require that the emissions tests include exhaust from the beginning of cold start. It is proved that 50%∼80% of HC and CO emissions are emitted during the cold start and the amount of unburned fuel from the crevices during starting is much higher than that under warmed engine conditions. The piston crevices is the most part of combustion chamber crevices, and results of mathematical simulations show that the piston crevice contribution to HC emissions is expected to increase during cold engine operation. Based on the transient HC test data and the double zone combustion model, this paper presents the study of the crevice HC Mechanism of the first firing cycle at cold start on an LPG SI Engine. A fast-response flame ionization detector (FFID) was employed to measure transient HC emissions of the first firing cycle.

Multi-spark discharge (MSD) ignition is widely used in high-speed internal combustion engines such as racing cars, motorcycles and outboard motors in attempts to achieve multiple sparks during each ignition. In contrast to transistor coil ignition (TCI) system, MSD system can be greatly shortened the charging time in a very short time. However, when the engine speed becomes higher, the ignition will be faster, electrical energy stored in the ignition system will certainly become less, especially for MSD system. Once the energy released into the spark plug gap can’t be guaranteed sufficiently, ignition will become more difficult, and it will get worse in some harsh environment such as strong turbulence or lean fuel conditions. With these circumstances, the risks of misfire and partial combustion will increase, which can deteriorate the power outputs and exhaust emissions of internal combustion engine.

This paper presents a study of LPG lean burn in a motorcycle SI engine. The lean burn limits are compared by several ways. The relations of lean burn limit with the parameters, such as engine speed, compression ratio and advanced spark ignition etc. are tested. The experimental results show that larger throttle opening, lower engine speed, earlier spark ignition timing, larger electrode gap and higher compression ratio will extend the lean burn limit of LPG. The emission of a LPG engine, especially on NOx emission, can be significantly reduced by means of the lean burn technology.

Gasoline Direct Injection (GDI) engines have attracted interest as automotive power-plants because of their potential advantages in down-sizing, fuel efficiency and in emissions reduction. However, GDI engines suffer from elevated unburned hydrocarbon (HC) emissions during start up process, which are sometimes worsened by misfires and partial burns. Moreover, as the engine is cranked to idle speed quickly in HEVs (Hybrid Electric Vehicle), the transients of quick starts are more dramatically than that in traditional vehicle, which challenge the optimization of combustion and emissions. In this study, test bench had been set up to investigate the GDI engine performances for ISG (Integrated Starter and Generator) HEVs during start up process. Based on the test system, cycle-controlled of the fuel injection mass, fuel injection timing and ignition timing can be obtained, as well as the cycle-resolved measurement of the HC concentrations and NO emissions.

This work presents the study of the methane jet flame in a pressurized vitiated co-flow burner (PVCB). The lift-off length and the stabilization of the methane jet flame under different environment pressures, co-flow temperatures, co-flow rates and jet velocities have been studied, and a chemical numerical simulation based on Gri-mech 3.0 was analyzed as well. The results could provide theoretical supports for the research of natural gas engine combustion stabilization control to increase its thermal efficiency. The experimental results show that the lift-off length decreases obviously (104.22mm to76.14mm) with the increase of the environment pressure (1to1.5bar, 1073K) and temperature (119.34mm to 43.74mm from 1058K to 1118K, 1bar), meanwhile, it also increases with the increment of the co-flow rate and jet velocity.

Many studies show that under diesel engine operating conditions, SCR reductant sprays will impinge on the wall of exhaust pipes. In order to understand this impinging process of SCR reductant spray, and to analyze what factors affect it, a test bench was set up by means of high speed video camera. At atmospheric pressure, SCR spray was injected on a heated metal wall, the impacts of wall temperature, injection pressure, injection height and angle on developing characteristics of SCR reductant spray after impinging on the heated wall have been researched and analyzed. The results show that the heated wall temperature has a great impact on the spray developing process, when wall temperature is lower than 405K, after water evaporated the crystallized urea will remain on the wall to block exhaust pipes. When wall temperature is higher, the atomization and evaporation of SCR reductant spray will be better, and the hydrolysis process of urea will be faster.

Spray behavior is regarded as one of main factors which influence engine performance, fuel consumption and emissions for diesel engine. In practice, spray characteristics from each orifice from a multi-hole nozzle are normally arranged symmetrically, while the hole-to-hole spray variation is unavoidable. This variation will cause spatial uneven distribution of spray and combustion degrade, which will be no longer inconsiderable in face of the more and more stringent emission rules. In this paper, two methods including spray macro-characteristics experiment and separated fuel mass measurement are employed to test the hole-to-hole spray variation of two six-hole symmetric VCO injectors of different brands, and experiments are operated under different conditions including different injection pressures, back pressures and injection durations.

One-dimensional transient modeling techniques are adapted to analyze the thermal behavior of lean-burn after-treatment systems when active flow control schemes are applied. The active control schemes include parallel alternating flow, partial restricting flow, and periodic flow reversal (FR) that are found to be especially effective to treat engine exhausts that are difficult to cope with conventional passive flow converters. To diesel particulate filters (DPF), lean NOx traps (LNT), and oxidation converters (OC), the combined use of active flow control schemes are identified to be capable of shifting the exhaust gas temperature, flow rate, and oxygen concentration to more favorable windows for the filtration, conversion, and regeneration processes. Comparison analyses are made between active flow control and passive flow control schemes in investigating the influences of gas flow, heat transfer, chemical reaction, oxygen concentration, and converter properties.

Diesel fueling and exhaust flow strategies are investigated to control the substrate temperatures of diesel aftertreatment systems. The fueling control includes the common-rail post injection and the external supplemental fuel injection. The post injection pulses are further specified at the early, mid, or late stages of the engine expansion stroke. In comparison, the external fueling rates are moderated under various engine loads to evaluate the thermal impact. Additionally, the active-flow control schemes are implemented to improve the overall energy efficiency of the system. In parallel with the empirical work, the dynamic temperature characteristics of the exhaust system are simulated one-dimensionally with in-house and external codes. The dynamic thermal control, measurement, and modeling of this research intend to improve the performance of diesel particulate filters and diesel NOx absorbers.

Combustion diagnostics of highly diluted mixtures are essential for the estimation of the combustion quality, and control of combustion timing in advanced combustion systems. In this paper, a novel fast response flame detection technique based on active plasma is introduced and investigated. Different from the conventional ion current sensing used in internal combustion engines, a separate electrode gap is used in the detecting probing. Further, the detecting voltage across the electrode gap is modulated actively using a multi-coil system to be slightly below the breakdown threshold before flame arrival. Once the flame front arrives at the probe, the ions on the flame front tend to decrease the breakdown voltage threshold and trigger a breakdown event. Simultaneous electrical and optical measurements are employed to investigate the flame detecting efficacy via active plasma probing under both quiescent and flow conditions.

In the recent decades, the emission and fuel efficiency regulations put forth by the emission regulation agencies have become increasingly stringent and this trend is expected to continue in future. The advanced spark ignition (SI) engines can operate under lean conditions to improve efficiency and reduce emissions. Under such lean conditions, the ignition and complete combustion of the charge mixture is a challenge because of the reduced charge reactivity. Enhancement of the in-cylinder charge motion and turbulence to increase the flame velocity, and consequently reduce the combustion duration is one possible way to improve lean combustion. The role of air motion in better air-fuel mixing and increasing the flame velocity, by enhancing turbulence has been researched extensively. However, during the ignition process, the charge motion can influence the initial spark discharge, resulting flame kernel formation, and flame propagation.

As the main power form of new energy vehicles, e-axle systems are has been widely used in passenger vehicles and commercial vehicles. A passenger car equipped with an e-axle, in constant speed and low torque conditions, there is a noticeable rattle noise, through experimental investigation and comparative analysis, it is confirmed that the connection spline of motor and reducer is the main influencing factor. Then, Through the qualitative analysis of simulation, it is found that both spline clearance and misalignment have an amplification effect on the motor speed, thereby stimulating the gear pair of the reducer to produce rattle. The amplification effect of spline clearance is stronger than that of spline misalignment.

This paper describes the application of CAE tools in the design optimization of a DCT and driveline system of a passenger vehicle, with emphasis on NVH performance. The multi-body dynamics simulation tools are employed for driveline system analysis. The MBD model consists of the engine, transmission, clutch, drive shafts, tires and vehicle. The wheel slip effects are considered in the calculation of shuffle frequencies. In the analysis of gear whine, the transmission housing, gears and shafts are modeled by detailed 3-D finite element models, so that the mesh stiffness of the gears and the housing support stiffness are described more accurately. The calculated velocity spectra of the housing are presented. The prediction of gear rattle in the transmission is carried out. The loose gear acceleration index and the averaged impact power of free gears are calculated to assess the rattle generation potential and the level of rattle severity.

It has been revealed by researches that lubricant properties have a great effect on the low-speed pre-ignition (LSPI) frequency in downsizing turbocharged direct-injection engines which are developed for better fuel economy. Droplets of lubricant or lubricant-gasoline mixture are considered to be the potential pre-ignition sources. Those droplets fly into the combustion chamber and ignite the gasoline-air mixture. To study lubricant droplets fundamentally, a novel set of droplet auto-ignition system is designed based on a Dibble Burner for this experiment. Influences of metallic additive contents, viscosities, lubricant diluted with gasoline and waste lubricant on the ignition delay of droplets are investigated by testing 12 groups of lubricants or lubricant-gasoline mixture. The equivalent diameter of each droplet generated by micro-syringes is around 2.1 mm. The co-flow temperature varies from 1123 K to 1223 K, and the experiments are carried out at atmospheric pressure.

Spark ignition systems with the capability of providing spark event with either higher current level or longer discharge duration has been developed in recent years to help IC engines towards clean combustion with higher efficiency under lean/diluted intake charge. In this research, a boosted current spark strategy was proposed to investigate the effect of spark discharge current level and discharge duration on the combustion process. Firstly, the discharge characteristics of a boosted current spark system were tested with a traditional spark plug under crossflow conditions, and results showed that the spark channel was more stable, and was stretched much longer when the discharge current was boosted. Then the boosted current strategy was used in a spark ignition engine operating under lean conditions. Boosted current was added to the spark channel with different timing, duration, and current levels.

Diesel Particulate Filters (DPF) are viable to reduce smoke from diesel engines. An oxidation process is usually required to remove the Particulate Matter (PM) loading from the DPF substrates. In cases when the engine exhaust temperature is insufficient to initiate a thermal regeneration, supplemental energy is commonly applied to raise the exhaust gas and/or the DPF substrate temperatures. A flow reversal (FR) mechanism that traps a high temperature region in the DPF substrate by periodically altering the gas flow directions has been identified to be capable of reducing the supplemental energy and thus to improve the overall thermal efficiency of the engine. However, extended operations with low exhaust temperature lowers the DPF boundary temperatures that defers the regeneration processes. Furthermore, the temperature fluctuations caused by the periodic FR operation also increase the thermal stress in the DPF.

Due to the advantages of low weight, low emissions and good fuel economy, downsized turbocharged gasoline direct injection (GDI) engines are widely-applied nowadays. However, Low-Speed Pre-Ignition (LSPI) phenomenon observed in these engines restricts their improvement of performance. Some researchers have shown that auto-ignition of lubricant in the combustion chamber has a great effect on the LSPI frequency. To study the auto-ignition characteristics of lubricant, an innovative single droplet auto-ignition test system for lubricant and its mixture is designed and developed, with better accuracy and effectiveness. The experiments are carried out by hanging lubricant droplets on the thermocouple node under active thermo-atmosphere provided by a small “Dibble burner”. The auto-ignition process of lubricant droplets is recorded by a high-speed camera.