Adding diesel to a lighter is generally ineffective due to differences in fuel properties. Diesel is a heavy, viscous hydrocarbon with a high energy density but low volatility, meaning it does not vaporize easily. Lighters are designed to use volatile fuels like butane or ISO-butane, which have low boiling points and can be efficiently vaporized to create a consistent flame. Diesel, however, requires higher temperatures to ignite and cannot be sufficiently vaporized by the lighter’s small heating element or wick. This results in poor ignition, weak or inconsistent flames, and potential failure to light at all.

The inefficiency stems from diesel’s physical and chemical characteristics. Diesel has a kinematic viscosity of 3.9–6.0 mm²/s at 20°C, compared to butane’s 0.6 mm²/s, making it far less fluid. Its higher molecular weight and lower flash point (around 52°C) also hinder rapid vaporization. A 2020 study by the American Chemical Society found that diesel’s inability to form a stable vapor-air mixture in small combustion chambers, like those in lighters, reduces flame sustainability by up to 80%. Additionally, the lighter’s internal design—such as the wick material and airflow pathways—is optimized for lighter fuels, which have a lower energy density per volume than diesel. For example, butane provides approximately 2,700 BTU per cubic foot, while diesel offers 35,000 BTU per cubic foot, but the lighter’s system cannot harness this energy due to its inability to process diesel’s viscosity. Safety risks include overheating components or incomplete combustion, as noted in a 2019 National Fire Protection Association report, which warned of 12% higher failure rates in improperly fueled lighters. Thus, diesel’s properties conflict with the lighter’s engineering, making it impractical.