Shijin Shuai’s research while affiliated with Tsinghua University and other places

In the present work, volatile organic compounds (VOCs) from vehicle exhaust and cooking fumes were investigated via simulation experiments, which covered engine emissions produced during gasoline direct injection (GDI) using two kinds of fuels and cooking emissions produced by preparing three domestic dishes. The distinct characteristics of VOCs emitted during the two processes were identified. Alkanes (73% mass fraction on average) and aromatics (15% on average) dominated the vehicle VOCs, while oxygenated VOCs (49%) and alkanes (29%) dominated the cooking VOCs. Isopentane (22%) was the most abundant species among the vehicle VOCs. N-hexanal (20%) dominated the cooking VOCs. The n-hexanal-to-n-pentanal ratio (3.68 ± 0.64) was utilized to identify cooking VOCs in ambient air. The ozone formation potential produced by cooking VOCs was from 1.39 to 1.93 times higher than that produced by vehicle VOCs, which indicates the significant potential contribution of cooking VOCs to atmospheric ozone. With the equivalent photochemical age increasing from 0 h to 72 h, the secondary organic aerosol formation by vehicle VOCs was from 3% to 38% higher than that of cooking VOCs. Controlling cooking emissions can reduce SOA pollution in a short time due to its higher SOA formation rate than that of vehicle VOCs within the first 30 h. However, after 30 h of oxidation, the amount of SOAs formed by vehicle exhaust emissions exceeded the amount of SOAs produced by cooking activities, implying that reducing vehicle emissions will benefit particle pollution for a longer time. Our results highlight the importance of VOCs produced by cooking fumes, which has not been given much attention before. Further, our study suggested that more research on semi-volatile organic compounds produced by cooking emissions should be conducted in the future.

Diesel engines face a challenge on environment pollutions, especially nitrogen oxides (NOx) and particle emissions. In recent years, advanced combustion modes were developed and fuels for different physical and chemical performances were investigated. Many researches showed that naphtha fuels well suited for compression ignition engines. In this paper, two reformates from naphtha fuels, named as High Reactivity Gasoline (HRG) and High Reactivity Gasoline blended with ethanol (HRE), and diesel were used to learn the effects on combustion and emissions of a single-cylinder compression-ignition (CI) engine. Experiments were conducted at a low load operating point, 1055 r/min-7.2 bar IMEP (gross indicated mean effective pressure) which could significantly show the effects of different fuels’ characteristics. A dual split fuel injection strategy was employed. In the experimental condition, fuel injection pressure, intake pressure, and exhaust gas recirculation (EGR) rate were maintained the same for all test fuels. Horiba MEXA-7200 and DMS500 were used to measure gas emissions and particle number (PN) emissions respectively. Results showed that HRG and HRE realized a stable combustion on diesel engine by using a two-stage injection strategy. HRE had the longest ignition delay leading to a single-stage heat release rate which was different from that with the other fuels. As a result, the trends of combustion and emission characteristics were unique. For HRE, the second injection timing (SOI2) dominated the maximum cylinder pressure rise rate (PRMAX) while it showed little effect on PRMAX using the other fuels. Fuel with low chemical reactivity could reduce the NOx emission and led to high CO and THC emissions. However, HRE had an overlong ignition delay led to an overlap of two combustion stages. The combustion was fast and the NOx emission became worse. In the experimental condition, the nucleation mode particles dominate the PN emissions. HRE and diesel had huge nucleation mode particle emissions due to the short combustion duration and the enhanced diffusion combustion, respectively. In conclusion, HRG had advantages on emissions which showed the lowest PRMAX, NOx and PN emissions and HRE had the advantage on engine working efficiency which could reach 47.8% in this study.

Today, the problem of energy shortage and climate change has urgently motivated the development of research engaged in improving the fuel efficiency of internal combustion engines (ICEs). Although many constructive alternatives—including battery electric vehicles (BEVs) and low-carbon fuels such as biofuels or hydrogen—are being put forward, they are starting from a very low base, and still face significant barriers. Nevertheless, 85–90% of transport energy is still expected to come from combustion engines powered by conventional liquid fuels even by 2040. Therefore, intensive passion for the improvement of engine thermal efficiency and decreasing energy loss has driven the development of reliable approaches and modelling to fully understand the underlying mechanisms. In this paper, literature surveys are presented that investigate the relative advantages of technologies mainly focused on minimizing energy loss in engine assemblies, including pistons and rings, bearings and valves, water and oil pumps, and cooling systems. Implementations of energy loss reduction concepts in advanced engines are also evaluated against expectations of meeting greenhouse gas (GHG) emissions compliance in the years to come.

A LNT (lean NO x trap) model coupled with EGR (exhaust gas recirculation) was developed based on the Langmuir–Hinshelwood mechanism to investigate the EGR effects on NO x adsorption pathway of LNT catalysts with temperature changed in range 150℃~550℃. Both the nitrate and nitrite adsorption paths were considered for the NO x storage process in the model as well as the spillover of stored NO x between Ba and Pt sites. The data and validation for modelling were from literatures of predecessors and our previous lean-burn gasoline engine experiment*. The model quantified the contributions of both nitrate route and nitrite route to the NO x storage with change of EGR rate (0%~30%) under raw emission atmosphere from tested gasoline engine. The model captured key feature of different trends of nitrate route and nitrite route with increasing temperature (150℃~550℃) under EGR rate varying from 0% to 25%. The LNT model provided insight of reaction mechanism for interpreting the behaviour of NO x storage with change of GER rate and temperature, which contributed to improve the NO x storage capacity when mapping EGR rate for lean-burn engine and catalyst operation strategy optimization.