Comparison of Retrofit Options for Carbureted Two-Stroke Engines

Abstract:

Carbureted two stroke engines are ubiquitous throughout the developing world. They are easy to operate, durable and preferred due to their low fare and personalized services. However, elevated levels of fuel consumption and emissions are problematic. Carbureted two stroke engines produce: high levels of unburned hydrocarbons (UHC), due to scavenging losses, carbon monoxide (CO), due to fuel rich operation, and particulate matter (PM) due to over–oiling. One common application for these engines is small taxis or “auto-rickshaws” in India. These commercial vehicles operate between 8 and 20 hours per day, further exacerbating the environmental impact. Despite development of new vehicles that employ better technology, the large number of in-use two stroke vehicles on road continue to pose a big challenge for air quality management in cities. Several retrofit options are available for these engines; two that are commercially available are Liquefied Petroleum Gas (LPG) and Direct Injection (DI) retrofits, both marketed as ‘environmentally friendly’ technologies.

This study compares the advantages of LPG retrofits and DI retrofits with the carbureted baseline. The study looks at Bajaj “Auto-rickshaw” three wheeler taxi’s from India. A field and lab comparison of emissions and efficiency is made between a carbureted baseline, two-common LPG retrofits, and a DI retrofit. The data was taken both on a chassis dynamometer and constant volume emissions sampling (CVS) system as well as using a portable emissions analyzer (PEMS).