tsi

TSI is an acronym that can refer to several concepts across science and engineering. Among its most widely recognized meanings are Total Solar Irradiance, a measure of the Sun’s energy reaching the Earth’s atmosphere, and Turbocharged Stratified Injection, a family of petrol engines branded by the Volkswagen Group.

Total Solar Irradiance (TSI) describes the solar energy per unit area incident on a plane perpendicular to the Sun at Earth's orbit, typically expressed in watts per square meter. The commonly cited solar constant is about 1361 W/m^2, though reported values vary with instrument calibration and processing. TSI is a key input for climate models and energy balance studies and serves as a reference for solar energy systems. In practice, the irradiance at Earth's surface is lower due to atmospheric absorption and scattering. Space-based radiometers on missions such as SORCE, SOHO, and PICARD provide direct measurements, and several composite records (PMOD, ACRIM, RMIB) exist. Long-term trends and gains in TSI have been subjects of scientific discussion and calibration debates.

Turbocharged Stratified Injection (TSI) refers to a class of petrol engines that combine turbocharging with direct fuel injection. This approach improves power output while enhancing fuel efficiency compared with naturally aspirated designs. The Volkswagen Group popularized the TSI branding in the mid-2000s, and the technology has been used across multiple marques, often with variations in boost, injection timing, and cooling. Early implementations faced challenges such as turbo lag and reliability concerns, leading to ongoing refinements in engine control and components.

Because the acronym TSI has multiple meanings, the intended definition depends on the context.