Webinar: How Dinex DiFlex Tackles Vibration, Heat Loss and Deposit Formation in Exhaust Systems

Dinex Group has developed DiFlex, a flexible exhaust coupling that combines mechanical decoupling, leak-tightness, thermal insulation and deposit protection within a single component. Konstantin Bondarev, Pipe Technology Solutions – R&D Leader, Dinex Group, explained the technology’s construction, operating principles and validation results during a technical webinar.

Flexible couplings in commercial vehicle exhaust systems must accommodate engine movement and vibration while preventing exhaust gas leakage and limiting heat loss. These requirements become particularly important in modern exhaust aftertreatment systems, where temperature management and diesel exhaust fluid (DEF) dosing influence emissions control performance.

Why conventional couplings require compromises

Flexible hoses and metal bellows are commonly used to accommodate movement between engines and exhaust aftertreatment systems. Flexible hoses offer multidirectional flexibility, including torsional movement, but require additional measures for leak-tightness and insulation.

Metal bellows provide a leak-tight metallic gas path and defined axial and lateral flexibility, although torsional movement and insulation require specific design provisions.

DiFlex combines these functions through a multilayer construction comprising an inner flexible profile, thermal insulation, a leak-tight sleeve and an outer metallic protective structure. Each layer performs a specific function while allowing the coupling to accommodate movement under operating conditions.

The inner profile permits axial, lateral and torsional displacement, while the insulation layer retains heat within the exhaust gas path. A flexible sealing sleeve prevents gas leakage during movement, and the outer metallic structure protects the internal layers against mechanical exposure.

Commercial vehicle exhaust connections experience repeated mechanical loads from engine vibration, movement and thermal expansion. The coupling must accommodate these forces without placing excessive stress on adjoining exhaust components or compromising its sealing function.

DiFlex provides flexibility in three directions: axial, lateral and torsional. Dinex identifies torsional compliance as a key difference from conventional metal bellows, which generally require dedicated design measures to accommodate twisting movement.

The coupling’s flexible sealing membrane moves with the structure, allowing the gas boundary to remain intact during displacement. Its insulation layer is also designed to retain its function while the coupling flexes.

Retaining heat and reducing deposit formation

Temperature management is particularly important in exhaust systems equipped with selective catalytic reduction (SCR) technology. Exhaust gas temperature influences the operation of the aftertreatment system, while DEF dosing introduces the possibility of deposits forming in cooler sections of the exhaust path.

DiFlex incorporates thermal insulation to reduce heat loss and limit external surface temperatures. In comparative thermal testing presented by Dinex, the coupling showed a lower temperature drop than the reference design over the test period.

The inner flexible profile also shields the flexible region from direct exposure to the exhaust flow. Together with the insulation layer, this arrangement is intended to reduce the risk of DEF crystallisation and deposits accumulating around the flexible section.

The combination is particularly relevant in exhaust layouts where DEF dosing takes place upstream of the coupling. Maintaining gas temperature while protecting the flexible region can help address deposit formation without sacrificing the movement capability of the connection.

Dinex presented validation results covering mechanical fatigue, elevated temperatures, exhaust flow and continuous DEF dosing. The mechanical validation programme included 10 million cycles at 500°C and a frequency of 5 Hz, with axial, lateral and torsional movement applied during testing.

A separate hot-flow and dosing validation covered five million cycles over 24 hours. Test conditions included temperatures between 180°C and 400°C, exhaust flow rates of 100–400 kg/h and continuous dosing.

Dinex reported zero litres per minute leakage before and after validation. The coupling also maintained flexibility below 150 N and retained a 30% extension capability following testing.

The results presented covered the coupling’s ability to retain sealing, flexibility and movement capability under the specified validation conditions.

Different constructions for different applications

DiFlex can be configured according to the operating environment and installation requirements. Dinex presented three construction options: open, protected and high-vibration.

The open construction is intended for protected installation locations where minimum external protection is required. The protected version uses a metallic outer hose to shield the internal layers while retaining mechanical flexibility.

For more demanding dynamic environments, the high-vibration construction incorporates an outer profile optimised for repeated movement and vibration exposure.

Dinex can also vary insulation thickness, coupling diameter, length and inner profile geometry. These parameters are selected according to heat-retention targets, available installation space, movement requirements and potential exposure to deposits.

Role in exhaust aftertreatment integration

DiFlex is intended for applications where mechanical movement, thermal management and sealing requirements must be addressed within the same exhaust connection.

By combining these functions, the coupling can reduce heat loss upstream of the aftertreatment system, limit external surface temperatures and protect the flexible region against deposits associated with DEF dosing.

The integrated construction also provides flexibility in exhaust system packaging, allowing manufacturers to select coupling configurations according to the available space and operating conditions.

For commercial vehicle manufacturers and exhaust aftertreatment suppliers, the technology offers a means of addressing several functional requirements through a single coupling architecture.

Dinex’s validation results provide the basis for assessing its mechanical and thermal performance, while application-specific testing will determine its suitability for individual exhaust system designs.

Established in 2002, the Emission Controls Manufacturers Association (ECMA) represents 21 global emission-control technology manufacturers and allied industries in India.

The association works with industry stakeholders, policymakers and regulators to promote cleaner mobility, advance emission-control technologies and support the development and implementation of stricter emission standards, including the proposed BS-7 norms.