The hitting streak ties him with Troy Tulowitzki and Nelson Cruz for the longest in the Major Leagues this season.
Encarnacion was the talk of baseball in 2014 when he tied the record for most home runs hit in May, with 16. That type of performance is tough to top, but his OPS so far in August is 1.255, which is even better than last May's 1.132.
"We were really waiting for Eddie to really break out in a big way," manager John Gibbons said. "You talk about May last year, where he was so hot with a record-setting month. You'd see signs of it, and he has still been very productive, but you were waiting for that one explosion and that run to really take off.
"I'm seeing it now, really after all the [July] trades, he's getting better and better. I think he's feeling it like the rest of the guys, he likes what's going on with the team, and he's getting sucked up in that, too, and that's helped him."
Encarnacion finished May 2014 with a .281 average, with the 16 homers, 33 RBIs and a .369 on-base percentage. The power numbers are down, but almost everything else is up. In 17 August games, Encarnacion is batting .397 with six home runs, 19 RBIs and a .446 on-base percentage.
Wednesday's grand slam was the eighth of his career and second of the season, with both coming against the Rangers. During the 21-game streak, he is batting .392, and 36 of his last 73 hits have gone for extra bases.
Encarnacion is a streaky hitter, but when he's in this type of groove, it usually causes nightmares for opposing pitchers.
"I'm just looking for my pitch, trying to be aggressive in the strike zone, looking for my pitch, and it has been great the way I've been seeing the ball the last couple of weeks," he said.
Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, follow him on Twitter @gregorMLB and Facebook, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.