6. Compressed Natural Gas and Hythane for On-road Passenger and Commercial Vehicles

This chapter discusses implementation of hydrogen-enriched compressed natural gas (HCNG, also called hythane) in automotive engines. Existing passenger vehicles (PV) and commercial vehicles (CVs) are mainly dependent on fossil fuels such as gasoline and diesel. Due to depleting fossil fuel reserves, stringent emission legislations and on-road fuel economy requirements, IC engines are required to use cleaner alternate fuels. Several prominent alternative fuels have emerged such as alcohols, biodiesel and LPG but none of them are widely accepted for large-scale commercial applications. However, most countries have implemented blending of gasoline with alcohol (up to 5–15% v/v) for commercial applications. Compressed natural gas (CNG) has also been widely successful as a commercial automotive fuel. Over last couple of decades, number of CNG vehicles on the roads has increased drastically worldwide. CNG as an automotive fuel is commercially implemented for PVs and heavy-duty CVs. Most important quality of CNG is its lower emissions and it is accepted as a clean transport fuel. However, CNG suffers from severe shortcomings, especially related to its chemical and physical properties such as lower diffusivity, lean-burn limits, high ignition energy requirement, lower flame speed and large flame quenching distance compared to hydrogen. To improvise the properties of CNG as well as for implementing hydrogen for automotive applications, drawbacks of CNG are countered with hydrogen blending. This mixture is known as hydrogen-enriched compressed natural gas (HCNG/H₂CNG or hythane). HCNG also improves feasibility of implementing hydrogen in automotive industry, which otherwise has serious safety concerns because of low ignition energy and wide flammability range of hydrogen. In this scenario, HCNG is fast emerging as a feasible alternative fuel to meet stringent emissions and fuel economy norms with minimal increase in cost and hardware of existing conventional gasoline/diesel engine.