No abstract

Diesel-piloted natural gas has been considered one of the most promising methods of using natural gas in a compression-ignition engine with few modifications, as this approach benefits from a high thermal efficiency resulting from a high compression ratio. This study experimentally investigated the impact of the natural gas substitution rate on the characteristics of combustion and emissions. Tests were performed under full-load operating conditions at a fixed speed of 1200 r/min with optimized injection timing, and the substitution rate of natural gas was varied with the fixed total fuel energy for different analyses. The in-cylinder pressure, pressure rise rate, heat release rate, cyclic variation of the maximum cylinder pressure (P max ) and emissions of HC, CO, NO x , and smoke were analyzed. The results indicate that P max and the maximum pressure rise rate initially increase and then decrease as the substitution rate of natural gas increases, whereas the heat release rate and standard deviation of P max increase. Moreover, HC and CO increase as the substitution rate of natural gas increases, whereas NO x and smoke emissions exhibit a trade-off trend.

In hydraulic mechanical transmission loaders, a hydraulic torque converter can prevent an engine from stalling due to overloading of the loader during the spading process; however, the hydraulic torque converter also reduces the loader's fuel economy because of its low transmission efficiency. To address this issue, the study designs an output-power-split transmission system that is applied to a hybrid loader. The designed transmission system removes the hydraulic torque converter in the power transmission system of a traditional loader and adopts a planetary gear set with a compact structure as the dynamic coupling element, thus allowing the output power of the loader to be split transmitted. During shoveling, the loader power-split transmission system based on a planetary gear set can prevent the motor from plugging and over-burning under conditions that ensure that the traction does not decrease. In addition, the transmission efficiency and loader fuel economy are higher in the proposed transmission system than in the power transmission system of a traditional loader. The test results show that the transmission efficiency of the designed system was 13.2% higher than that of the traditional hydraulic mechanical transmission loader.

Vehicle emissions standards and regulations remain weak in high-altitude regions. In this study, vehicle emissions from both the New European Driving Cycle and the Worldwide harmonized Light-duty driving Test Cycle were analyzed by employing on-road test data collected from typical roads in a high-altitude city. On-road measurements were conducted on five light-duty vehicles using a portable emissions measurement system. The certification cycle parameters were synthesized from real-world driving data using the vehicle specific power methodology. The analysis revealed that under real-world driving conditions, all emissions were generally higher than the estimated values for both the New European Driving Cycle and Worldwide harmonized Light-duty driving Test Cycle. Concerning emissions standards, more CO, NOx, and hydrocarbons were emitted by China 3 vehicles than by China 4 vehicles, whereas the CO2 emissions exhibited interesting trends with vehicle displacement and emissions standards. These results have potential implications for policymakers in regard to vehicle emissions management and control strategies aimed at emissions reduction, fleet inspection, and maintenance programs.

No abstract

Limitations still remain among vehicle emissions standards and regulations about high-altitude areas at altitude over 2400 m. In view of high vehicle-use intensity for buses, on-road measurements were performed on four heavy-duty diesel vehicles by employing a portable emissions measurement system (PEMS) in Lhasa, with an average elevation of approximately 3650 m. The result indicated that under real-world driving conditions of Lhasa, compared with China III buses, China IV buses did not show excellent emission performance consistently. For example, carbon monoxide (CO) emission factor of China III-5.2L buses is 2.4 times of China IV-5.2L buses, while the nitrogen oxides (NOx) is only 36% of China IV-5.2L. Furthermore, an operating mode binning and a micro-trips method are used to link real-world emissions of each vehicle to driving conditions. For China III-5.2L and China IV-5.2L buses, we found strong correlations between relative emission factors of carbon dioxide (CO2) and NOx and average speed. However, these correlations for China IV-7.8L bus were less strong. This phenomenon proves that the role of traffic conditions in affecting road driving emissions would be mitigated when selective catalytic reduction (SCR) functioning properly. This study have potential implications for policymakers concerning vehicle emissions management and control strategies, such as promotion of alternative fuel with in-used buses, aimed at emissions reduction.

Intake throttling has been verified as an effective approach to increase the exhaust temperature of diesel engines, which could benefit the catalytic efficiency aftertreatment. To better understand the influence of intake throttling on the combustion characteristics and exhaust emissions of light-duty diesel engines operating under idle mode, a light-duty diesel engine was experimentally investigated. This study is a follow-on to previous studies on the effect of throttling on light-duty diesel engine exhaust temperatures and emissions. Tests were conducted at a fixed idle speed of 1100 rpm, and the throttle position and intake manifold air pressure (MAP) were varied. The in-cylinder pressure, pressure rise rate, heat release rate (HRR), in-cylinder temperature, exhaust temperature, and regular gaseous emissions were analyzed. The results indicated that under the influence of intake throttling, the MAP decreased from 101 kPa under wide-open-throttle (WOT) conditions to 52.5 kPa under the heaviest throttling conditions, and the exhaust temperature increased from 100 °C to 200 °C, with a fuel penalty associated with the increase in the pumping indicated mean effective pressure (IMEP). The in-cylinder pressure continuously declined with decreasing MAP, while the HRR generally increased with increasing MAP. Under WOT conditions, the ignition delay decreased, while the combustion duration decreased under heavier throttling conditions. The in-cylinder temperature with throttling was higher than that under WOT conditions, and after post-injection treatment, the in-cylinder temperature exhibited an increasing trend with decreasing MAP. The CO2, CO, NOx, and HC emissions increased with increasing throttling amounts.

No abstract