When their prototype cooking stove passed its first trial with flying colors in Ghana, the American designers Jonathan Cedar and Alex Drummond expected it to be equally successful in the next round of tests in India. But then they discovered that very different types of food would be cooked on it.

“The staple dish in Ghana is banku, a starchy mass of corn or cassava dough, and luckily it suited our stove,” Mr. Cedar recalled. “Where we got stuck in India was with flat breads, which need a very hot, very diffuse flame. When people saw the stove, they were like: ‘Oh no, no, no.”’

There was a simple solution: designing different tops for the stove to suit the cooking requirements of various regions. But other problems have proved less tractable in the five years that Mr. Cedar and Mr. Drummond have been developing the BioLite home stove as a safer, less expensive means of cooking for the three billion people throughout the world who cook on open fires.

Mr. Cedar, 31, and Mr. Drummond, 53, are among the growing number of designers who are applying their skills and entrepreneurial zeal to empower the billions of people who lack basic products and services. Developing a cheaper, cleaner method of cooking could make a dramatic difference to many lives. As well as curbing the environmental damage caused by fumes from indoor cooking fires, it promises to reduce the 1.9 million premature deaths linked to them each year. It could also spare people, mostly women and girls, from spending several hours a day collecting fuel, rather than working or studying. Finally, the BioLite stove includes a charging facility, which should save time and money for the millions of people whose homes are located outside electricity grids and who have to walk long distances — and pay hefty fees — to charge their cellphones.