Experimental investigations of combustion, performance and emission characteristics of a hydrogen enriched natural gas fuelled prototype spark ignition engine Gaurav Verma, Rajesh Kumar Prasad, Rashmi A. Agarwal, Siddhant Jain, Avinash Kumar Agarwal ⇑ Engine Research Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India highlights  Effect of hydrogen enrichment of natural gas on engine performance.  Fuels with different H/C ratios (4, 4.22, 4.5, 4.85, 5.33 and 1) were investigated.  Brake thermal efficiency was superior for test fuel with H/C: 4.5.  P max increases with increasing H/C ratio of the test fuels.  HRR was highest for hydrogen along with shortest ignition delay. article info Article history: Received 27 September 2015 Received in revised form 5 March 2016 Accepted 8 March 2016 Available online 15 March 2016 Keywords: Hydrogen enriched natural gas H/C ratio NOx Spark ignition engine Combustion abstract In this study, spark ignition of hydrogen enriched natural gas (HCNG), a fast emerging alternative gaseous fuel, was experimentally investigated in a suitably modified single cylinder spark ignition (SI) engine. Port fuel injection of the HCNG engine using a high volume flow rate solenoid injector, controlled by a customized injector control unit and electronic control unit (ECU) was done and the fuel injection timings and duration were controlled for each load. Fuels with different H/C ratios in the final HCNG mixture were investigated for their engine performance, emissions and combustion characteristics. Engine inves- tigations were carried out at constant engine speed of 1500 rpm for different H/C ratios (4, 4.22, 4.5, 4.85, 5.33 and 1). Spark timing was kept constant (32° bTDC) for all test blends. Relative air–fuel ratio (RAFR) was kept constant for all loads during the experiments in order to avoid misfire at lower engine load. Hydrogen exhibited higher pressure peak (P max ) but lower maximum brake torque (MBT) compared to other test fuels due to lower knocking limit. Brake thermal efficiency (BTE) was superior for test fuel with H/C: 4.5. NOx emissions were higher for test fuel with H/C: 4.22 and relatively lower for hydrogen com- pared to baseline natural gas. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Rapid increase in energy demand and resulting consumption of conventional fossil fuels has led to rapid depletion of underground carbon energy reserves and increasing fuel prices. This has increased dependency of all major global economies on gulf coun- tries. In addition, it has also adversely affected air quality signifi- cantly, resulting in severe environmental degradation and climate change. Conventional fossil fuels are responsible for emis- sion of harmful species such as unburned hydrocarbons (HC), car- bon monoxide (CO), oxides of nitrogen (NOx), particulate matter (PM) and carbon dioxide (CO 2 ). These pollutants have severe health effects on human body and the global environment. Therefore commercialization of prominent low carbon or carbon free alterna- tive fuels such as natural gas and hydrogen is necessary for the sur- vival of humanity. These fuels have potential to reduce harmful green-house gas (GHG) emissions and could displace a portion of conventional liquid fossil fuels. Both these fuels however offer different challenges for their uti- lization in internal combustion (IC) engines. For example, hydro- gen requires very low ignition energy therefore utilization of hydrogen in IC engines can potentially cause pre-ignition and backfire [2]. Use of hydrogen also leads to low power output and constraints the operating load range of the engine because of very low density of hydrogen, which in-turn reduces the volumetric http://dx.doi.org/10.1016/j.fuel.2016.03.022 0016-2361/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +91 512 2597982; fax: +91 512 2597408. E-mail address: akag@iitk.ac.in (A.K. Agarwal). Fuel 178 (2016) 209–217 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel