Raja Yoga is a step by step, systematic and scientific approach for one to follow. Of my limited understanding; tapas for me is practices; the practices that we do for our growth and understanding of inner dimensions of life.
All the yamas and niyamas are for the mind, for the inner purification rather than for our gross selves. These are the commitments we make to ourselves to train the mind so that it becomes an aid rather than an obstacle on this journey of life. It has little to do with projecting them on the outside and pretending how sattvic we are becoming. But when doing tapas (practices) we purify our mind of its fickleness; it reflects in our nature and our surrounding environment. It’s so organic that it hardly noticeable when it’s happening but now when I look at my mere self now to the one that it was a year ago; there are subtle positive changes. This feed back helps one to track and calibrate the process we are in. To be conscious and mindful of the practices that we are following in our life is tapas. And it definitely includes preceding yamas-niyamas : ahimsa, saucha, satya, santosh, ashteya
Newton’s Third Law: Every action has equal and opposite reaction.
Swami Rama always says even if we just sit and even pretend to meditate; it will be beneficial. So every action has an effect. And every action in our life is tapas. Now though beneficial; it may not be necessarily progressive if we are doing our actions/practices without awareness.
Doing practices with mindful conscious awareness is the key as it will enable you to experience how even a simple act of watching the flow of your breath can take you beyond body and breath, can give you a glimpse that something lies beyond.