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Hybrid powertrain has been proven to be an effective fuel-saving technology in commercial vehicles, but many hybrid commercial vehicles still use conventional diesel engines, resulting in limited fuel savings. The main purpose of this study is to enhance the thermal efficiency of a dedicated hybrid diesel engine focusing on the characteristic operating conditions. Via fundamental thermodynamics process analysis of internal combustion engine, steel piston with high compression ratio, air system involving two-stage turbocharger(2TC) with an intercooler, and late intake valve closing(IVC) timing are proposed to improve the thermal efficiency of the engine. Experimental results show that high compression ratio and lower thermal conductivity of the combustion chamber surface lead to lower heat release rates, requiring optimization of piston profile to accelerate the mixing rate. Besides, high compression ratio also leads to higher mechanical losses.

To achieve autonomous driving, many advanced control methods have been conducted. This paper proposes a driver model coupling lateral and longitudinal control for curve driving based on dual-level model predictive control (MPC). During the curve driving, actual expert drivers can conduct vehicle’s lateral motion control in coordination with longitudinal control, so a safer and smoother driving performance can be achieved. In order to better reflect this behavior in the control model for autonomous driving, a dual-level MPC is applied to improve trajectory following ability on curve road. Firstly, a lateral following module based on two-wheel bicycle model and MPC is established. Then, the lateral decision is used as the input of another longitudinal control module based on MPC. In this way, longitudinal control module will ensure the vehicle keeps at a stable motion state during the whole curve. Finally, the effectiveness of the proposed method is verified by a simulated experiment.

How to generate a reasonable path for automatic parking assist has been extensively studied. However, it is still a huge challenge to design a path planner that can handle tight space environments for all common parking scenarios. The things need to be considered in the process of path planning algorithm design, including generate a path quickly and low computational costs and collision-free path, make the problem even more difficult to be solved. In this paper, a path planning algorithm based on hybrid A-star and RS algorithm is proposed. The algorithm introduces the concept of guiding points which we can directly generate collision-free path through the RS algorithm, and the guiding point are calculated offline using hybrid A-star algorithm for various working scenarios. And the algorithm was tested and validated by the simulation and vehicle test in two common parking scenarios.

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.

This work numerically investigates the detailed combustion kinetics of partially premixed combustion (PPC) in a diesel engine under three different premixed ratio fuel conditions. A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict PPC combustion under various operating conditions. The experimental results showed that the increase of premixed ratio (PR) fuel resulted in advanced combustion phasing. To provide insight into the effects of PR on ignition delay time and key reaction pathways, a post-process tool was used. The ignition delay time is related to the formation of hydroxyl (OH). Thus, the validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how PR change the formation of OH during the low-to high-temperature reaction transition. The reaction pathway analyses of the formations of OH before ignition time were investigated.

OH, soot and temperature distributions of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (Ta) was set as 773 K, and the wall temperature (Tw) was set as 523 K, 673 K, 773 K, respectively. Three different injection pressures (Pi) of 60 MPa, 100 MPa, 160 MPa, and the ambient pressures (Pa) of 4 MPa were applied. The OH spatial distributions of wall-impinging spray were measured by the method of OH chemiluminescence imaging. Two-color pyrometry was applied to evaluate the spatial distributions of KL factor and flame temperature of wall-impinging spray. The results reveal that, OH chemiluminescence is observed in the region near the impingement point firstly. The regions of high OH chemiluminescence intensity and high KL factor appear in the location near the wall surface along the whole combustion process.

Based on the temperature and pressure in the cylinder of GDI (Gasoline Direct Injection) engines under the common operating conditions, jets´ characteristics of gasoline and iso-octane at different fuel temperatures under the high ambient temperature were studied by means of high-speed photography and striation method. It is found that the supercritical gasoline jet shows the morphological collapse of jet center and the protrusion of the front surface, but the iso-octane jet doesn´t. Meanwhile, as the fuel temperature rises, the flash boiling and the interference between adjacent plumes affect the gasoline jet, and cause the center of the jet to form a high-speed and low-pressure zone, hence the air entrainment in this region contributes to the collapse of jets. The collapse and convergence of jets´ morphology are the main reasons for the change of penetration and cone angle.

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.

Liquefied natural gas (LNG) engine could provide both reduced operating cost and reduction of greenhouse gas (GHG) emissions. Stoichiometric operation with EGR and the three-way catalyst has become a potential approach for commercial LNG engines to meet the Euro VI emissions legislation. In the current study, numerical investigations on the knocking tendency of several combustion chambers with different geometries and corresponding performances were conducted using CONVERGE CFD code with G-equation flame propagation model coupled with a reduced natural gas chemical kinetic mechanism. The results showed that the CFD modeling approach could predict the knock phenomenon in LNG engines reasonably well under different thermodynamic and flow field conditions.

The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity.

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.

Changan has upgraded its 1.6 L naturally aspirated GDI engine to meet future fuel economy and emission regulation base on its previous 1.6 L naturally aspirated GDI engine, the major upgrades include a high compression ratio of 13, 35Mpa direct injection system, cooled external EGR, thermo management module,and extensive measures to reduce friction. With this new engine, the vehicle fuel consumption is reduced by 9%, and meet the China 6b emission standard without GPF.

Gasoline partially premixed combustion shows the potential to achieve clean and high-efficiency combustion. Injection strategies show great influence on in-cylinder air flow and in-cylinder fuel distribution before auto-ignition, which can significantly affect the combustion characteristics and emissions. This study explored the effects of various injection strategies, including port fuel injection (PFI), single direct injection (DIm), double direct injection (DIp+DIm) and port fuel injection coupled with a direct injection (PFI+DIm) on the combustion characteristics and emissions in a modified single cylinder heavy-duty diesel engine fueled with 92# gasoline at low load. The investigation consists of two parts. Firstly, the comparison among PFI, PFI+DIm, and DIp+DIm strategies was conducted at a fixed CA50 to explore the effects of PFI+DIm and DIp+DIm strategies on the thermal efficiency and combustion stability.

The flame structure and combustion characteristics of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (Ta) was set to 773 K. The wall temperatures (Tw) were set to 523 K, 673 K and 773 K respectively. Three different injection pressures (Pi) of 600 bar, 1000bar and 1600bar, two ambient pressures (Pa) of 2 MPa and 4 MPa were applied. The flame development process of wall-impinging spray was measured by high-speed photography, which was utilized to quantify the flame luminosity intensity, ignition delay and flame geometrical parameters. The results reveal that, as the wall temperature increases, the flame luminosity intensity increases and the ignition delay decreases.

Gasoline direct injection (GDI) engine technology is now widely used due to its high fuel efficiency and low CO2 emissions. However, particulate emissions pose one challenge to GDI technology, particularly in the presence of fuel injector deposits. In this paper, a 4-cylinder turbocharged GDI engine in the Chinese market was selected and operated at 2000rpm and 3bar BMEP condition for 55 hours to accumulate injector deposits. The engine spark timing, cylinder pressure, combustion duration, brake specific fuel consumption (BSFC), gaseous pollutants which include total hydro carbon (THC), NOx (NO and NO2) and carbon dioxide (CO), and particulate emissions were measured before and after the injector fouling test at eight different operating conditions. Test results indicated that mild injector fouling can result in an effect on engine combustion and emissions despite a small change in injector flow rate and pulse width.

The dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion could achieve high efficiency and low emissions over a wide range of operating conditions. However, further high load extension is limited by the excessive pressure rise rate and soot emission. Polyoxymethylene dimethyl ethers (PODE), a novel diesel alternative fuel, has the capability to achieve stoichiometric smoke-free RCCI combustion due to its high oxygen content and unique molecule structure. In this study, experimental investigations on high load extension of gasoline/PODE RCCI operation were conducted using late intake valve closing (LIVC) strategy and intake boosting in a single-cylinder, heavy-duty diesel engine. The experimental results show that the upper load can be effectively extended through boosting and LIVC with gasoline/PODE stoichiometric operation.

Wall temperature in GDI engine is influenced by both water jacket and gas heat source. In turn, wall temperature affects evaporation and mixing characteristics of impingement spray as well as combustion process and emissions. Therefore, in order to accurately simulate combustion process, accurate wall temperature is essential, which can be obtained by conjugate heat transfer (CHT) and piston heat transfer (PHT) models based on mapping combustion results. This CHT model considers temporal interaction between solid parts and cooling water. This paper presents an integrated methodology to reliably predict in-cylinder combustion process and temperature field of a 2.0L GDI engine which includes engine head/block/gasket and water jacket components. A two-way coupling numerical procedure on the basis of this integrated methodology is as follows.

On-board fuel reforming offers a prospective clean combustion mode for the engines. The flexible cylinder engine strategy (FCE) is a new kind of such mode. In this paper, the combustion of the primary reference fuel of PRF90 was theoretically investigated in a homogeneous charge compression ignition engine to validate the FCE mode, mainly focusing on the ignition delay time, the flame speed, and the emissions. The simulations were performed by using the CHEMKIN2.0 package to demonstrate the fuel reforming process in the flexible cylinder, the cooling effect on the reformed products, and the combustions of the mixture of the fresh fuel and the reformed products in the normal cylinders. It was found that the FCE mode decreased the ignition delay time of the fuel by about 35 crank angles at a typical engine condition.

Reactivity controlled compression ignition (RCCI) is a potential combustion strategy to achieve high engine efficiency with ultra-low NOx and soot emissions. Fuel stratification can be used to control the heat release rate of RCCI combustion. But the in-cylinder combustion process of the RCCI under different fuel stratification degrees has not been well understood, especially at a higher engine load. In this paper, simultaneous measurement of natural flame luminosity and emission spectra was carried out on a light-duty optical RCCI engine under different fuel stratification degrees. The engine was run at 1200 revolutions per minute under a load about 7 bar indicated mean effective pressure (IMEP). In order to form fuel stratification degrees from low to high, the common-rail injection timing of n-heptane was changed from -180° CA after top dead center (ATDC) to -10° CA ATDC, while the iso-octane delivered in the intake stroke was fixed.

This research presents an experimental study of the laminar burning combustion and emission characteristics of premixed methane -dissociated methanol-air mixtures in a constant volume combustion chamber. All experiments were conducted at 3 bar initial pressure and 373K initial temperature. The dissociated methanol fractions were from 20% to 80% with 20% intervals, and the equivalence ratio varied from 0.6 to 1.8 with 0.2 intervals. The images of flame propagation were visualized by using a schlieren system. The combustion pressure data were measured and exhaust emissions were sampled with a portable exhaust gas analyzer. The results show that the unstretched laminar burning velocities increased significantly with dissociated methanol enrichment. The Markstein length decreased with increasing dissociated methanol fraction and decreasing equivalence ratio.