Fossil fuels are still one of the worlds major sources of energy. Because of their limited natural availability, however, renewable resources like biodiesel provide an attractive contribution to meet the growing demand for energy supply. A significant problem associated with the use of biodiesel as fuel for diesel engines is a higher NOx emission tendency. It is known that additives can mitigate NOx emissions from biodiesel and biodiesel blends. Therefore, this study investigated the effect of the additives benzoic and pivalic hydrazide using an ignition bomb (Advanced Fuel Ignition Delay Analyser - AFIDA (ASG Analytik-Service Gesellschaft). In addition, the hydrazides were tested with a Farymann single cylinder four-stroke diesel engine. In contrast to results reported elsewhere previously, it was found that the tested hydrazides did not show any significant influence on NOx emissions under the test conditions. (C) 2016 Elsevier Ltd. All rights reserved.