We give improved lower bounds for M(n, d), for various positive integers d and n with d < n, where M(n, d) is the largest number of permutations on n symbols with pairwise Hamming distance at least d. Permutation arrays are used for constructing error correcting permutation codes, which have been proposed for power-line communications. We describe two techniques, which use a modified Kronecker product and a tiling operation, called doubling. Our techniques improve the size of permutation arrays, and improve lower bounds on M(n, d), for infinitely many n and d, d < n.