--- title: "Hybrid vehicle and environment impact" subject: "Energy Environment and Society" chapter: 5 key: "semester_7/energy_environment_and_society:hybrid-vehicle" source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/hybrid-vehicle site: BCT Engineering --- # Hybrid vehicle and environment impact Energy Environment and Society · Chapter 5: Energy Storage - Asked in: 2071 Chaitra, 4 marks; 2070 Chaitra, 2+2 marks (asked 2 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/hybrid-vehicle - Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-5 ## Question Write briefly about the working principle of hybrid vehicles. Also discuss the environment impacts. ## Short answer Hybrid vehicles combine an internal combustion engine with an electric motor and battery, using regenerative braking and engine shut-off at idle to improve efficiency. They reduce fuel use and emissions like CO2 and NOx, though battery production involves mining impacts and still rely on fossil fuels; overall lifecycle emissions are lower than conventional cars. ## Answer A **hybrid electric vehicle (HEV)** combines an internal combustion engine (ICE) with one or more electric motors and a battery, so that each works where it is most efficient. #### Working principle - At low speed or start, the electric motor drives the car (the engine is off, no idle emission). - At normal and high speed, the engine drives the wheels and also charges the battery through a generator. - During hard acceleration, both engine and motor work together. - During braking and coasting, **regenerative braking** converts kinetic energy into electricity and stores it in the battery. - An electronic controller decides the best mix, and the engine is shut off at stops (start-stop). #### Types 1. **Series hybrid:** the engine only drives a generator; the motor drives the wheels. 2. **Parallel hybrid:** both engine and motor can drive the wheels directly. 3. **Series-parallel (power-split) hybrid:** combination (Toyota Prius). 4. **Plug-in hybrid (PHEV):** larger battery that can be charged from the grid, with an electric-only range. ```text Fuel tank -> [Engine] --+--> [Transmission] -> Wheels | ^ [Generator]-> [Battery]<->[Motor] ``` #### Environmental impacts **Positive** - Higher fuel economy (30–50% better than a conventional car) and lower CO₂, NOₓ, CO and PM per km. - Quieter in the city and lower dependence on imported petroleum (relevant for Nepal). - PHEVs charged with hydroelectricity have very low emissions. **Negative** - Battery production uses lithium, cobalt and nickel, with mining impacts and energy use. - Battery disposal and recycling issues; heavier vehicle and higher cost. - Still burns fossil fuel and emits pollutants, unlike a pure battery EV; emissions depend on how electricity is made. Overall, the life-cycle emissions of hybrids are lower than those of petrol or diesel cars. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a hybrid drive at low speed or start? A. The electric motor drives the car with the engine off B. Engine alone drives with high idling C. Both engine and motor at full power D. The car is towed Answer: A. This avoids idle emissions. (Key point: Low-speed operation) 2. What does regenerative braking do? A. Converts battery energy into heat B. Converts kinetic energy into electricity stored in the battery C. Burns extra fuel D. Increases engine speed Answer: B. It recovers energy otherwise lost as heat. (Key point: Regenerative braking) 3. What defines a series hybrid? A. Both engine and motor drive wheels directly B. Only grid charging C. The engine only drives a generator and the motor drives the wheels D. Engine drives wheels only Answer: C. Parallel hybrids let both drive the wheels. (Key point: Series hybrid) 4. Which is a negative environmental impact of hybrids? A. Higher CO2 per km than petrol cars B. No battery disposal issue C. They emit no pollutants at all D. Battery production uses lithium, cobalt and nickel, with mining impacts Answer: D. Overall life-cycle emissions are still lower than petrol or diesel cars. (Key point: Environmental trade-off) ## Related in Energy Environment and Society - [Battery and working principle](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abattery-working-principle) — Energy Environment and Society, chapter 5 - [Environmental impacts of wind machine](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Awind-machine-environment-impact) — Energy Environment and Society, chapter 4 - [Health impacts of indoor air pollutants](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aindoor-air-pollutants-health) — Energy Environment and Society, chapter 4 - [Impact of technology, sustainable development](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Atechnology-impact-society-sustainable) — Energy Environment and Society, chapter 1 - [Technology transfer and impact on life](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Atechnology-transfer-life-impact) — Energy Environment and Society, chapter 1 - [Appropriate technology and impact on society](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aappropriate-technology-society-impact) — Energy Environment and Society, chapter 1 ## Related in other subjects - [Hybrid vehicles, autonomy levels and IoT](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Ahybrid-autonomy-iot-notes) — Automotive Technology, chapter 12 - [Human-vehicle-environment system; driver characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Ahve-system-driver-physical-characteristics) — Transportation Engineering II, chapter 1 - [Impact of technology on environment and society](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Atech-impact-environment-society) — Technology, Environment and Society, chapter 1, asked 2× - [FHMA principle and hybrid techniques for near-far](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-hybrid-near-far) — Wireless Communication, chapter 7