DESIGN, FABRICATION AND TESTING OF A FUEL-EFFICIENT ENGINE TRANSMISSION SYSTEM OF A PROTOTYPE VEHICLE AND BODY AERODYNAMICS EVALUATION

ABSTRACT
This project entails the design construction and test evaluation of an energy efficient go-cart engine and transmission system.
A target of 100km/l of fuel is set, having the knowledge that weight plays a major role in the efficiency of any vehicle using internal combustion engines; and also the aerodynamics of the vehicle body design is equally important as well. Aluminium profiles are used to construct and fabricate the chassis while wooden board is used for floor covering. Care is taken to reduce any excessive weights by cutting off parts that do not contribute to the structural integrity of the vehicle or which its contribution is highly negligible.
A CRF70 series engine was selected for the design with a net torque of 7.1Nm, with the required torque compensated for using a gear ratio of 1:3. The vehicle design acquiesces with the Shell Eco-Marathon Global Rules for the prototype gasoline category; which implies that there are design requirements and rules which must be met and not to be exceeded. For instance, a need for idling when the engine is cranked. The engine is installed behind the bulkhead separating the driver compartment from the engine compartment and rubber dampers of known damping coefficient are used to check the effect of vibration of the engine. A fuel tank of 250ml is used as reservoir for the gasoline while a chain drive mechanism is used to transmit power from the engine to the rear-wheel shaft on which the rear wheel is mounted; this in turn moves the entire vehicle. Care is taken to ensure fine tuning of the carburettor to avoid so much fuel consumption. After series of testing, the vehicle participated in the just concluded 2016 Shell Eco Marathon Challenger event held in South Africa which is one of the most genuine student engineers’ competition in the world where students in universities all over the world are challenged to design, fabricate and drive the ultimate energy efficient vehicles.
A result of 52.54km/l of fuel was recorded at the event computed using standard international algorithms as against 48km/l which was estimated. This implies acceleration, temperature of fuel and aerodynamic drag are all factors that contribute to the efficiency of any vehicle. This result of 52.52km/l is about 52.54% of the set target.
From the results, for a better performance an injector type engine should be used, that is the carburettor should be replaced by electronic fuel injection kits. Carbon fibre would