An investigation into Volkswagen practices revealed two of the company’s top engineers are behind the installation of engine software designed to mask diesel emissions to meet clean-air standards. Ulrich Hackenberg, Audi’s chief engineer, and Wolfgang Hatz, developer of Porsche’s winning Formula One engines, were considered two of Germany’s best and brightest engineers. The two were also among those suspended in the wake of the emissions-test cheating scandal last month. Hackenberg and Hatz were tapped to helm research and development at Volkswagen shortly after Martin Winterkorn became CEO in January 2007. The auto company said as many as 11 million vehicles were equipped with a “defeat device,” or software that reduces tailpipe emissions only when the car is being tested.