EXPERIMENTAL INVESTIGATION ON USE OF CNG AND DI-ETHYL ETHER IN HCCI ENGINE

Abstract

India is at a crucial stage where it must balance the need for rapid economic growth with energy security and environmental protection. More than 85% of the country’s crude oil demand is currently met through imports, creating both economic and strategic risks. At the same time, rising levels of air pollution and greenhouse gas emissions from the transport sector demand immediate solutions. In response, the Government of India has introduced several ambitious policies, including the Panchamrit commitments at COP26, the promotion of a gas-based economy, the National Biofuel Policy, and the enforcement of Bharat Stage VI (BS-VI) emission norms. These initiatives collectively highlight the urgent requirement for clean, fuel-flexible, and cost-effective engine technologies that can reduce dependence on fossil fuels and deliver ultra- low emissions. This work investigates Homogeneous Charge Compression Ignition (HCCI), an advanced low- temperature combustion strategy known for high efficiency and near-zero emissions. A conventional single-cylinder diesel engine was modified to operate in HCCI mode. For this purpose, a custom-designed external fuel vaporizer and injector system was developed and integrated with a data acquisition platform. This indigenous setup allowed precise thermal control and homogeneous charge preparation, both of which are critical for stable HCCI operation. The engine was systematically tested across a wide range of operating conditions, covering loads from 0–100% and fuel substitution ratios from 0–100%, in order to simulate diverse, real-world applications. The experimental program focused on three fuel pathways: conventional diesel operation, compressed natural gas (CNG) operation, and a novel dual-fuel strategy combining di-ethyl ether (DEE) with CNG. Diesel was used as a baseline to establish performance and emission vii benchmarks. CNG, which is central to India’s gas economy initiative, offered the advantage of lower NOx emissions but suffered from limitations such as poor ignition quality, unstable combustion, and higher unburned hydrocarbon (UHC) emissions. The introduction of DEE as an ignition promoter in combination with CNG addressed these challenges effectively. DEE, being a high-cetane oxygenated biofuel, improved the ignition characteristics of the lean CNG–air mixture, leading to more controlled combustion phasing, extended HCCI operability, and significant reductions in emissions. The results demonstrated that the DEE–CNG HCCI strategy outperformed both diesel and CNG- only operation. Quantitatively, DEE–CNG achieved up to a 9.6% increase in brake thermal efficiency and a 14.3% reduction in specific energy consumption compared to CNG HCCI mode, showing clear improvements in energy conversion efficiency. From an emission perspective, NOx levels were reduced by more than 83% relative to diesel baseline, while UHC emissions decreased by around 20% compared to CNG-only operation. Importantly, these gains were achieved without relying on expensive after-treatment technologies such as selective catalytic reduction, proving the in-cylinder effectiveness of the approach in meeting BS-VI standards. In conclusion, this study establishes DEE–CNG dual-fuel HCCI as a practical, retrofittable, and scalable clean combustion solution for compression ignition engines. By integrating an indigenously producible oxygenated biofuel with a cleaner gaseous fuel, the research offers a pathway that directly supports India’s long-term goals of reducing crude oil imports, improving energy security, and creating a low-carbon, sustainable transport future. The findings provide both technological validation and policy relevance, positioning this strategy as a strong candidate for future automotive and stationary engine applications in India.