The　direct　combustion　of　by-product　hydrogen　is　a　promising　way　for　reducing　costs　and　greenhouse　emissions.　Coke　oven　gas　(COG)　which　is　mainly　composed　of　H2,　CH4　and　CO　is　a　major　source　of　by-product　hydrogen　that　is　suitable　to　be　adopted　by　internal　combustion　engines.　This　paper　investigated　the　COG　combustion　in　a　spark-ignition　engine　with　Miller　cycle.　To　get　an　overview　of　by-product　hydrogen　combustion　properties,　two　kinds　of　COG　compositions　with　the　maximum　and　minimum　hydrogen　fractions　were　tested.　The　excess　air　ratio　(λ)　was　raised　from　stoichiometric　to　the　lean　limit　to　explore　the　capability　of　COG　on　improving　the　engine　performance　under　a　common-driving　speed　of　1500　rpm　and　part　load　conditions.　The　test　results　indicated　that　the　engine　fueled　by　COG　with　higher　hydrogen　fractions　could　gain　concentrated　heat　release　period,　extended　lean　burn　limit,　reduced　HC　and　CO2　emissions,　and　enhanced　working　capability　only　at　ultra-lean　conditions.　The　properly　increased　λ　availed　improving　engine　efficiency　and　lowering　HC　emissions.　The　peak　indicated　thermal　efficiency　of　38.6%　was　acquired　at　the　λ　of　1.2,　while　the　lowest　HC　emissions　of　only　32　ppm　was　gained　at　the　λ　of　1.4.　Under　ultra　lean　conditions,　NO　emission　dropped　to　near　zero,　and　CO　from　the　by-product　hydrogen-fueled　engine　was　negligible　for　all　tested　ranges.　An　interesting　trend　of　peak　pressure　correlated　crank　angle　versus　λ　was　also　found　in　this　study.　©　2023　Hydrogen　Energy　Publications　LLC