SI
SI turns up in 2 fields: metrology, automotive. Here is what it means to the people in each one.
SI in metrology
International System of Units, the coherent set of seven base units on which all traceable measurement rests.
SI stands for the International System of Units: the second, metre, kilogram, ampere, kelvin, mole and candela, plus the derived units built from them. Each base unit is defined by fixing the numerical value of a constant of nature, such as the Planck constant for the kilogram and the elementary charge for the ampere. Metrological traceability ultimately means relating a result to realizations of these units.
"Customer wants traceability to the SI, not to some vendor's in-house standard, so it has to go through an accredited chain."
SI in automotive
An engine design that relies on an electrical arc to ignite the air-fuel mixture.
Spark ignition identifies internal combustion engines that use spark plugs to initiate combustion, distinguishing them from compression ignition engines. These powerplants compress a homogenous mixture of fuel and air, requiring a precise high-voltage spark to trigger the power stroke. The term frequently appears in engineering literature and emissions regulations to categorize gasoline, ethanol, and natural gas engines.
"The emissions standard for heavy SI engines changed again this year."