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基于北斗轨迹数据的拖拉机CO2与NOx排放预测模型构建与清单估算

Prediction model and inventory estimation of CO2 and NOx emissions from tractors based on Beidou trajectory big data

  • 摘要: 为深入研究拖拉机污染物与温室气体排放特征与构建排放清单,助力农机绿色转型与“双碳”目标实现,该研究基于北斗轨迹数据与PEMS实测数据,构建了拖拉机油耗、CO2与NOx排放预测模型,并估算了全国的作业排放清单。基于北斗轨迹数据中字段完整的样本,结合拖拉机速度、方向、转速、扭矩等多维特征,构建油耗预测特征集,并采用残差深度神经网络模型预测油耗,模型拟合优度R2为0.75,平均绝对百分比误差(mean absolute percentage error, MAPE)为24.46%。针对特征字段缺失的数据,进一步基于作业时长与作业距离构建油耗预测特征,并采用多种机器学习算法建立预测模型。对比结果表明,LightGBM模型效果最优(R2为0.77,MAPE为39.28%)。通过开展拖拉机排放试验,构建CO2和NOx排放预测模型,系统比较不同机器学习算法与特征组合的预测性能。结果显示,以发动机油耗、转速、扭矩、功率、大气温度、湿度作为输入特征时,支持向量机为CO2排放预测最优模型(R2 为0.95,MAPE为5.98%)。LightGBM为NOx排放预测最优模型(R2 为 0.86,MAPE为13.78%)。若仅基于油耗特征进行排放预测,则CO2和NOx的最优模型分别为LightGBM(R2为0.94,MAPE为8.01%)与随机森林(R2为0.77,MAPE为17.9%)。通过集成轨迹数据、油耗和排放预测模型,定量估算全国安装北斗终端的拖拉机作业总排放量。该研究可为大范围农机作业的碳排放与污染物排放管理提供方法支撑与数据支持,推动中国农业绿色转型与“双碳”目标实现。

     

    Abstract: Agricultural machinery is one of the most significant sources of non-road mobile emissions in recent years. Yet accurate estimation of its carbon and pollutant emissions is often hindered by the fuel consumption data and localized emission factors. In this study, a prediction framework was developed for tractor fuel consumption, CO2, and NOx emissions from tractors. Massive BeiDou trajectory data were also integrated with portable emission measurement system (PEMS) measurements and the national operational emission inventory. 1) The samples were incorporated with complete fields from the BeiDou trajectory data and multidimensional features, such as the tractor speed, direction, engine speed, and torque. A feature set was constructed to predict the fuel consumption. A feature engineering process was conducted on the dataset of trajectory samples with complete fields from the 2023 summer harvest. The trajectories were segmented into kinematic fragments with a time step of 100s. A Residual Deep Neural Network (ResDNN) model with a 21-layer structure was employed to predict fuel consumption, with an R2 of 0.75 and a MAPE of 24.46%. Fuel consumption features were further constructed for the missing feature fields, according to the operational duration and distance. Various algorithms of machine learning were used for the predictive models. Light Gradient Boosting Machine (LightGBM) model performed best (R2=0.77, MAPE=39.28%). 2) Localized emission models were established. PEMS tests were then conducted on four typical China IV standard tractors with the rated powers of 51.5, 58.8, 88.2, and 177 kW under varying engine loads. According to the experimental data, machine learning algorithms (ridge regression, random forest, decision tree, SVM, and LightGBM) were compared to construct emission prediction models using multi-dimensional input features. The evaluation results indicated that the ResDNN model achieved the best performance for fuel consumption prediction with the features (R2=0.75, and MAPE=24.46%), effectively resolving the gradient degradation in deep networks. In the simplified feature set, the LightGBM model performed optimally (R2=0.77, and MAPE=39.28%). Support Vector Machine was identified as the optimal model for CO2 emissions (R2=0.95, MAPE=5.98%) prediction, while LightGBM performed best for NOx emissions (R2=0.86, MAPE=13.78%). Importance analysis revealed that instantaneous fuel consumption and engine speed were the most critical determinants for CO2 emission, whereas environmental parameters shared a higher contribution to NOx prediction. Finally, these models were applied to the trajectory data of 870,192 tractors equipped with BeiDou terminals during the 2023 summer harvest (May 25 to June 25). A high-resolution national emission inventory was estimated after application. The total fuel consumption was 47.01×106 L, thus generating 128.21×103t of CO2 and 281.9t of NOx. The average daily emissions per tractor were 147.33 kg for CO2 and 0.32 kg for NOx. Spatially, the emissions were concentrated in major agricultural provinces, such as Jiangsu, Henan, and Heilongjiang. Temporally, the emission peaks coincided perfectly with the busy farming rhythm. This finding can provide support data for carbon and pollutant emissions from large-scale agricultural machinery in green agriculture.

     

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