Last year's World Cup runners-up went into the game knowing victory would secure a last-four spot after previous wins over New Zealand and Pakistan.
Raj struck an assured 51 as India posted a total of 145-6 that was always likely to be too strong for Ireland, and the tournament's lowest-ranked team struggled to 93-8 in reply as Radha Yadav finished with three for 25.
The 35-year-old Raj, India's all-time record runscorer in T20s, laid the foundations for victory with a 67-run stand for the opening wicket with Smriti Mandhana, and after the game she played down injury fears after struggling with a knee problem.
"I'm sure my knee will get better," she said. "Today the wicket was quite challenging. The pitch was soft. And playing slower bowlers was difficult, but the partnership with Smriti was crucial."
India face Australia on Saturday to decide who finishes top of Group B, before playing the semi-finals on November 22.
Raj struck an assured 51 as India posted a total of 145-6 that was always likely to be too strong for Ireland