Renewable and Sustainable Energy Reviews · 2018

Efficient, cleaner combustion in hydrogen-enriched natural gas engines

Application of hydrogen enriched natural gas in spark ignition IC engines: from fundamental fuel properties to engine performances and emissions

Hydrogen enrichment can accelerate flame propagation and extend lean engine operation, offering opportunities to improve efficiency and reduce carbon emissions. This review connects fundamental fuel properties with engine performance, emissions and operating parameters to examine where these benefits can be realized.

The motivation

Lean operation of natural gas engines is constrained by slow flame propagation and cycle-to-cycle variability, making efficiency and emission control a coupled challenge. Hydrogen improves fuel reactivity, but the benefits depend on blend composition, combustion conditions and engine calibration. The review examines how changes in fuel properties translate into practical engine performance.

The approach

This literature review focuses on spark-ignition engines fueled by hydrogen-enriched natural gas. It first examines ignition delay, laminar burning velocity and flammability limits, then assesses engine experiments on power, fuel economy, cyclic variability and emissions. Engine-modeling studies help connect these observations with hydrogen fraction, air–fuel ratio, spark timing and compression ratio, identifying their interactions and optimization needs.

In-cylinder velocity vectors (top) and temperature contours (bottom) at different crank angles during the intake process. Original Fig. 38; reproduced in the review from Zaker et al. [172].

Key findings

Hydrogen’s lower ignition-energy requirement and faster burning promote early flame-kernel development and flame propagation, improving lean combustion stability and reducing cyclic variability. Extending the lean operating limit is a major route to efficient, lower-emission HCNG operation.
Compared with natural gas alone, hydrogen enrichment generally favors lower unburned-hydrocarbon, CO and CO₂ emissions, but higher combustion temperatures can increase NOₓ. Lean combustion and spark timing therefore need to be optimized together with hydrogen fraction to balance efficiency and emissions.
Efficiency and power benefits vary with operating conditions because improved combustion competes with wall heat loss and changes in the inducted mixture’s volumetric heating value. Hydrogen fraction, spark timing and compression ratio require coordinated optimization; high hydrogen fractions also warrant attention to pre-ignition, knock and backfire.

About this paper

Fuwu Yan, Lei Xu, Yu Wang

Renewable and Sustainable Energy Reviews · 2018 · 82(Part 1) · 1457–1488

Publisher record (DOI)