Experimental analysis of engine cooling capacity at different altitudes: a case study for biarticulated gas engine bus at high altitude

The demand for mass public transportation is growing on the major urban areas worldwide along with stricter demands on exhaust gas emission levels driven by society’s concern on the environment, leading to the development of sustainable transport solutions. Some of the solutions to reduce emission levels, such as electrified powertrains, may not be affordable for emergent markets due to the necessity of investments on infrastructure as well as high costs of some technologies. Bogotá city in Colombia is renewing its bus rapid transit (BRT) fleet and aims to reduce emission levels in its operation. Therefore, the development of a biarticulated bus driven by a compressed natural gas (CNG) Otto engine can be a sustainable solution for such application reducing both emission levels and fuel costs (compared to a Diesel model). However, the development of a cooling system for such bus becomes a challenge due to several factors that have a negative impact on cooling performance such as: high gross train weight (GTW); high altitude application; CNG Otto engine (compared to a Diesel model) and limited space for radiators/coolers on a front engine layout. Since tests during development phase could not be carried out at high altitude, engine cooling simulations were carried out for different vehicle configurations with varying ambient pressure to obtain a correction curve for engine cooling capacity at different barometric pressures. Then, development tests were carried out at low altitude on a prototype bus and later verification measurements were carried out at high altitude on a demonstration bus. Results from the measurements presented good correlation with the correction curve obtained by simulations and therefore can be applied in future developments.