I. Case Background: Sludge Removal Challenges in Haikou’s Humid and Hot Climate As a tropical coastal city, Haikou receives an average annual rainfall of approximately 1,600 mm, with the rainy season concentrated from May to October. Urban drainage networks thus face frequent cleaning and sludge removal tasks. In Q3 2025, a municipal sanitation department launched a procurement initiative for a batch of Dongfeng single-cab, blue-plate, 5-cubic-meter sludge suction trucks, with a budget capped at around RMB 125,000 per unit (based on publicly available tender information). Previously deployed older models suffered from severe chassis corrosion and aging sealing components, resulting in declining operational efficiency. This procurement therefore placed special emphasis on corrosion resistance, high-load operational stability, and engine compatibility under humid and hot conditions. After multiple rounds of technical and commercial evaluation, the Dongfeng single-cab sludge suction truck solution offered by Chengli Special Purpose Vehicle Co., Ltd. (“Chengli”) stood out. The vehicle features an original Dongfeng chassis, with the superstructure manufactured at Chengli’s Suizhou plant. It is fully compliant with national type-approval regulations (e.g., extended model series CLW5070GSSD6), enabling standard registration and annual inspection. In line with local procurement practices, the contract price was approximately RMB 105,000 per unit (tax-inclusive, delivered price), including upgraded anti-corrosion coating services. II. Engine Comparison: Selecting Among 85 kW, 100 kW, and 120 kW Options Sludge suction operations involve complex working conditions: maneuverability is essential in narrow urban alleys, while sustained loads—such as sludge pumping and high-pressure flushing—must also be accommodated. For this procurement, Dongfeng D-series engines were selected, offering three power configurations: 85 kW, 100 kW, and 120 kW. The comparison below is based on Chengli’s internal product database and MIIT type-approval parameters (reference model CLW5070GSSD6): | Parameter | 85 kW (~116 hp) | 100 kW (~136 hp) | 120 kW (~163 hp) | |-----------|------------------|-------------------|-------------------| | Reference Engine Model | Dongfeng D4.0NS6B** | Dongfeng D4.5NS6B** | Dongfeng D6.7NS6B** | | Displacement (L) | ~4.0 | ~4.5 | ~6.7 | | Max Torque (N·m) | ~400 | ~500 | ~600 | | Typical Application Scenario | Plain-city areas, light-duty sludge removal | Hilly cities, standard load operations | High-altitude/mountainous regions, heavy-duty/high-load operations | | Fuel Consumption (L/100 km, MIIT reference) | ~10–12 | ~12–14 | ~14–17 | | High-Altitude Adaptability (≥2,000 m elevation) | Significant power loss | Marginal usability | Minimal power loss; recommended | As shown in the table: the 85 kW engine offers lower fuel consumption (~10–12 L/100 km), making it ideal for routine, light-duty operations in plain cities like Haikou; the 100 kW option delivers greater power reserve, better suited for high-demand pumping during the rainy season; while the 120 kW variant excels in mountainous or heavy-load scenarios—but at higher fuel consumption (~14–17 L/100 km). Given that Haikou’s operational area is predominantly flat terrain and cost-efficiency was prioritized, the 85 kW configuration was selected. To ensure sufficient power reserve during prolonged rainy-season operations, Chengli equipped the vehicle with an intercooled turbocharging system. III. Anti-Corrosion and Sealing Component Design for Humid and Hot Environments Haikou’s high temperature and humidity (annual average relative humidity >80%) combined with salt-laden coastal air pose significant challenges to vehicle chassis, superstructures, and sealing components.