36
Measurement and Testing UPDATES AND ADVANCEMENTS IN OCTANE TESTING
Introduction: The automobile is a revolutionary invention that requires no further introduction. Equally as impactful was its subsequent popularization of gasoline. However, its discovery in 1859 was uneventful, as it was discarded as a byproduct of crude oil refi ning1
. It would remain as such
until the invention of automobile engines in 1892, which required gasoline as its primary fuel source2
. By the 1920s, millions of gasoline-
powered cars populated the United States. Moreover, an equal number of gasoline service stations opened up across the nation1
To this day, gasoline continues to dominate automotive fuel3
Figure 1: Three octane numbers differentiating three different gasoline types of varying stability 9
. . , and countless developments
in gasoline production and its refi nery have ensured that the fuel keeps pace in potency and effi ciency with the industries it powers.
O
ne of the most signifi cant testing procedures for gasoline is the Octane test, also known as the engine knock test4
.
In this test, gasoline blends are measured for their propensity to knock. Knock occurs from the premature combustion of the air-fuel mixture in an internal combustion engine, leading to undesirable and damaging high-pressure shock waves and a characteristic knocking sound5
whereas MON is the gasoline’s performance in more intensive conditions (around 900 rpm and intake air at 149℃)7
, and octane
testing is a process by which both numbers and the gasoline’s overall octane rating is measured and determined. Octane testing is a theoretically simple process. In a specialty CFR engine, the fuel is observed under standardized operating conditions. The compression ratio of the engine is then increased, which in turn increases the pressure and temperatures during combustion,
hence increasing the propensity of a fuel to knock. When the engine knocks at a certain intensity, the associated compression ratio is then compared to a reference fuel blend of iso-octane and n-heptane, which knocks at the same intensity for the compression ratio. The octane number of the fuel is the blend of iso-octane in that fuel8
. Then, relating to the reference fuels,
the specifi c RON or MON of the fuel is determined as conditions for the tests differ in engine speed and idle air temperatures6
.
With both ratings determined, the octane number posted on fuel pumps is given as the average of the RON and MON.
As mentioned, octane testing for MON and RON are two separate processes. Therefore, separate testing machines are employed, each confi gured toward separate tests. Current devices allow RON and MON tests on the same engine, but many scientists still prefer using separate machines tailored to each6
. To consolidate
research efforts, the American Society for Testing Materials (ASTM) has designated standards for both testing processes, among many others. As such, this paper will refer to RON and MON testing by their designated method names: ASTM-D2699 for RON testing of engine fuel, and ASTM-D2700 for MON testing of engine fuel10
.
. Octane tests and their numbers
hold signifi cant value to the refi nement and effi cacy of gasoline as a whole. And though people likely do not understand the intricacies of octane testing, car owners are guaranteed to understand the octane numbers on gasoline pumps. This paper illustrates the importance and relevancy of both octane testing and octane numbers, noting the process’s unique strengths and discussing several recent advancements that hold positive implications for future octane engine testing.
Octane Ratings, and Octane Testing:
Firstly, it is important to defi ne keywords and processes before elaborating further. All forms of gasoline are assigned an octane rating (AKA octane number), typically seen in gas pumps such as Figure 1, with higher octane ratings indicating more stable fuels6
. Octane numbers are an average of two octane rating
methods: Motor Octane Number (MON) and Research Octane Number (RON). RON is a measure of the gasoline’s performance in gentler conditions (around 600 rpm and intake air at 49℃)
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Figure 2: A combination octane rating unit engine octane. This unit (left) is able to determine both MON and RON values. Due to the nature of the device, both tests can be operated using the same chamber. A close-up of the carburetor is shown (right)
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