Cold and hot WHTC (World harmonized Transient-State Cycle) were separately run on the engine test bed for a heavy-duty natural gas engine fuelled with high calorific value natural gas and low calorific value natural gas. The particle emissions including PN10 (number of particles above 10nm) and PN23 (number of particles above 23nm) were measured. The results show that the transient emission of PN10 and PN23 have basically the same trends. The weighted specific emission of PN10 is 21.6 times of PN23. Cold start PN emissions account for a relatively large proportion. Fuel property has a great influence on the PN emissions of natural gas engines. The increase of carbon-containing fuels such as methane and ethane in the fuel gas will lead to a rapid increase in PN emissions especially in the cold start process. It is extremely important to strengthen the control of sub-23nm particulate emissions for heavy-duty natural gas engines.

A dump truck with a maximum designed total mass of 24500 kg was selected to measure the emission characteristics of pollutants and carbon dioxide (CO2) under fully-loaded and unloaded conditions at the same simulated road with different road slope, same driver and vehicle model by using the engine-inthe- loop methodology. The results show that driving at gradient road will result in an increase in power and total emissions. The brake specific emissions of gaseous pollutant and CO2 are lower at gradient road, while the brake emission of particle number are higher at gradient road. Road slope affects exhaust temperature so as to affect nitrogen oxide (NOx) emissions. Under unloaded conditions, long-slope conditions are more likely to cause an increase in NOx emissions.

Due to the issues of low flame speed and high CH₄ emissions for a natural gas engine, investigations into the partial oxidation fuel reforming (POFR) method used in natural gas engines to blend H₂ have become increasingly valuable. In this paper, the combustion process, engine performance, and emissions of a natural gas engine with fuel-reforming gases blended together have been numerically studied. The results show that a higher fuel-reforming ratio can effectively improve the engine combustion performance, especially at lean-burn conditions. Combustion with reformed gases can increase the thermal efficiency by almost 2% at the full-load condition, whereas fuel reforming significantly affects the natural gas engine’s power performance. Furthermore, CH₄ and NO_X emissions decrease significantly with increasing fuel-reforming ratio. In conclusion, fuel reforming for a natural gas engine has a promising future in reducing greenhouse gas emissions and improving economic performance.

Hardware-in-the-loop (HIL) technology combines physical hardware with virtual models to achieve efficient closed-loop simulation of automotive systems, demonstrating significant advantages in the development of automotive emissions and energy consumption. This paper reviews the current applications of three HIL technologies, including powertrain-in-the-Loop (PIL), engine-in-the-Loop (EIL), and Virtual Test Bed (VTB). It also explores their role in addressing the increasingly stringent regulations on emissions and energy consumption. Research indicates that PIL technology can significantly improve the efficiency with which hybrid powertrain control strategies are verified by integrating real powertrains with virtual environments. EIL technology enables the high-precision simulation of real-world emissions at low hardware cost. VTB technology, meanwhile, significantly reduces the calibration period by leveraging high-precision models and intelligent algorithms. These three technologies form a comprehensive development and verification chain, covering everything from components to vehicles. However, HIL technology still faces challenges relating to model accuracy, system complexity and cost. Therefore, the most suitable technology should be selected based on development objectives, timeframe, and budget.