Auto-ignition characteristics and kinetic modeling study of PODE3/n-heptane blends

Polyoxymethylene dimethyl ethers (PODE n ) are promising oxygenated additives for diesel engines due to their high cetane number and low soot emissions. However, the auto-ignition characteristics of PODE 3 blended with diesel surrogate fuels like n -heptane remain unclear, especially under low-to-intermediate temperature conditions (600–1000 K). In this work, the ignition delay times (IDTs) of PODE 3 / n -heptane blends (10–40 % PODE 3 molar fraction) were measured in a rapid compression machine (RCM) under stoichiometric conditions ( φ = 1.0), pressure of 10 bar, and temperatures ranging from 600 to 1000 K. Results show that the IDT decreases significantly with higher PODE 3 content, particularly above 800 K. While below 700 K, the effect of PODE 3 addition on the IDTs was less pronounced. A merged kinetic model combining validated PODE 3 and n -heptane mechanisms accurately captured the IDT trends with varying fuel compositions and their negative temperature coefficient (NTC) behaviors. Kinetic analyses revealed that PODE 3 accelerates n-heptane's first-stage ignition by enhancing radical accumulation (e.g., ȮH) through H-atom abstraction. Sensitivity analysis identified HȮ2 radical dynamics as critical in controlling system reactivity, with PODE 3 exhibiting a stronger promotion effect than n-heptane at higher temperatures. Reaction pathway analysis further indicated that temperature elevation shifts fuel consumption toward PODE 3 -dominated β -scission reactions, generating CH 2 O and H 2 O 2 , which decompose to ȮH radicals and accelerate ignition. These findings provide critical insights into optimizing PODE 3 -blended fuels for advanced engine designs. • Ignition delay times of PODE 3 /n-heptane blends are measured. • A chemical kinetic model of PODE 3 /n-heptane blends is developed and validated. • Reactivity-promoting effect of PODE 3 shows a unique temperature dependency. • Interaction mechanism between PODE 3 and n-heptane is revealed.