This review paper published in 2004 outlines the pharmacokinetic differences of L carnitine and acetyl-L-carnitine in the body.
References:
Rebouche C. J. (2004). Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism. Annals of the New York Academy of Sciences, 1033, 30–41. https://doi.org/10.1196/annals.1320.003